1 =================================== 1 ===================================
2 Documentation for /proc/sys/kernel/ 2 Documentation for /proc/sys/kernel/
3 =================================== 3 ===================================
4 4
5 .. See scripts/check-sysctl-docs to keep this 5 .. See scripts/check-sysctl-docs to keep this up to date
6 6
7 7
8 Copyright (c) 1998, 1999, Rik van Riel <riel@n 8 Copyright (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
9 9
10 Copyright (c) 2009, Shen Feng<shen@cn.fu 10 Copyright (c) 2009, Shen Feng<shen@cn.fujitsu.com>
11 11
12 For general info and legal blurb, please look 12 For general info and legal blurb, please look in
13 Documentation/admin-guide/sysctl/index.rst. 13 Documentation/admin-guide/sysctl/index.rst.
14 14
15 ---------------------------------------------- 15 ------------------------------------------------------------------------------
16 16
17 This file contains documentation for the sysct 17 This file contains documentation for the sysctl files in
18 ``/proc/sys/kernel/``. 18 ``/proc/sys/kernel/``.
19 19
20 The files in this directory can be used to tun 20 The files in this directory can be used to tune and monitor
21 miscellaneous and general things in the operat 21 miscellaneous and general things in the operation of the Linux
22 kernel. Since some of the files *can* be used 22 kernel. Since some of the files *can* be used to screw up your
23 system, it is advisable to read both documenta 23 system, it is advisable to read both documentation and source
24 before actually making adjustments. 24 before actually making adjustments.
25 25
26 Currently, these files might (depending on you 26 Currently, these files might (depending on your configuration)
27 show up in ``/proc/sys/kernel``: 27 show up in ``/proc/sys/kernel``:
28 28
29 .. contents:: :local: 29 .. contents:: :local:
30 30
31 31
32 acct 32 acct
33 ==== 33 ====
34 34
35 :: 35 ::
36 36
37 highwater lowwater frequency 37 highwater lowwater frequency
38 38
39 If BSD-style process accounting is enabled the 39 If BSD-style process accounting is enabled these values control
40 its behaviour. If free space on filesystem whe 40 its behaviour. If free space on filesystem where the log lives
41 goes below ``lowwater``\ % accounting suspends 41 goes below ``lowwater``\ % accounting suspends. If free space gets
42 above ``highwater``\ % accounting resumes. ``f 42 above ``highwater``\ % accounting resumes. ``frequency`` determines
43 how often do we check the amount of free space 43 how often do we check the amount of free space (value is in
44 seconds). Default: 44 seconds). Default:
45 45
46 :: 46 ::
47 47
48 4 2 30 48 4 2 30
49 49
50 That is, suspend accounting if free space drop 50 That is, suspend accounting if free space drops below 2%; resume it
51 if it increases to at least 4%; consider infor 51 if it increases to at least 4%; consider information about amount of
52 free space valid for 30 seconds. 52 free space valid for 30 seconds.
53 53
54 54
55 acpi_video_flags 55 acpi_video_flags
56 ================ 56 ================
57 57
58 See Documentation/power/video.rst. This allows 58 See Documentation/power/video.rst. This allows the video resume mode to be set,
59 in a similar fashion to the ``acpi_sleep`` ker 59 in a similar fashion to the ``acpi_sleep`` kernel parameter, by
60 combining the following values: 60 combining the following values:
61 61
62 = ======= 62 = =======
63 1 s3_bios 63 1 s3_bios
64 2 s3_mode 64 2 s3_mode
65 4 s3_beep 65 4 s3_beep
66 = ======= 66 = =======
67 67
68 arch 68 arch
69 ==== 69 ====
70 70
71 The machine hardware name, the same output as 71 The machine hardware name, the same output as ``uname -m``
72 (e.g. ``x86_64`` or ``aarch64``). 72 (e.g. ``x86_64`` or ``aarch64``).
73 73
74 auto_msgmni 74 auto_msgmni
75 =========== 75 ===========
76 76
77 This variable has no effect and may be removed 77 This variable has no effect and may be removed in future kernel
78 releases. Reading it always returns 0. 78 releases. Reading it always returns 0.
79 Up to Linux 3.17, it enabled/disabled automati 79 Up to Linux 3.17, it enabled/disabled automatic recomputing of
80 `msgmni`_ 80 `msgmni`_
81 upon memory add/remove or upon IPC namespace c 81 upon memory add/remove or upon IPC namespace creation/removal.
82 Echoing "1" into this file enabled msgmni auto 82 Echoing "1" into this file enabled msgmni automatic recomputing.
83 Echoing "0" turned it off. The default value w 83 Echoing "0" turned it off. The default value was 1.
84 84
85 85
86 bootloader_type (x86 only) 86 bootloader_type (x86 only)
87 ========================== 87 ==========================
88 88
89 This gives the bootloader type number as indic 89 This gives the bootloader type number as indicated by the bootloader,
90 shifted left by 4, and OR'd with the low four 90 shifted left by 4, and OR'd with the low four bits of the bootloader
91 version. The reason for this encoding is that 91 version. The reason for this encoding is that this used to match the
92 ``type_of_loader`` field in the kernel header; 92 ``type_of_loader`` field in the kernel header; the encoding is kept for
93 backwards compatibility. That is, if the full 93 backwards compatibility. That is, if the full bootloader type number
94 is 0x15 and the full version number is 0x234, 94 is 0x15 and the full version number is 0x234, this file will contain
95 the value 340 = 0x154. 95 the value 340 = 0x154.
96 96
97 See the ``type_of_loader`` and ``ext_loader_ty 97 See the ``type_of_loader`` and ``ext_loader_type`` fields in
98 Documentation/arch/x86/boot.rst for additional 98 Documentation/arch/x86/boot.rst for additional information.
99 99
100 100
101 bootloader_version (x86 only) 101 bootloader_version (x86 only)
102 ============================= 102 =============================
103 103
104 The complete bootloader version number. In th 104 The complete bootloader version number. In the example above, this
105 file will contain the value 564 = 0x234. 105 file will contain the value 564 = 0x234.
106 106
107 See the ``type_of_loader`` and ``ext_loader_ve 107 See the ``type_of_loader`` and ``ext_loader_ver`` fields in
108 Documentation/arch/x86/boot.rst for additional 108 Documentation/arch/x86/boot.rst for additional information.
109 109
110 110
111 bpf_stats_enabled 111 bpf_stats_enabled
112 ================= 112 =================
113 113
114 Controls whether the kernel should collect sta 114 Controls whether the kernel should collect statistics on BPF programs
115 (total time spent running, number of times run 115 (total time spent running, number of times run...). Enabling
116 statistics causes a slight reduction in perfor 116 statistics causes a slight reduction in performance on each program
117 run. The statistics can be seen using ``bpftoo 117 run. The statistics can be seen using ``bpftool``.
118 118
119 = =================================== 119 = ===================================
120 0 Don't collect statistics (default). 120 0 Don't collect statistics (default).
121 1 Collect statistics. 121 1 Collect statistics.
122 = =================================== 122 = ===================================
123 123
124 124
125 cad_pid 125 cad_pid
126 ======= 126 =======
127 127
128 This is the pid which will be signalled on reb 128 This is the pid which will be signalled on reboot (notably, by
129 Ctrl-Alt-Delete). Writing a value to this file 129 Ctrl-Alt-Delete). Writing a value to this file which doesn't
130 correspond to a running process will result in 130 correspond to a running process will result in ``-ESRCH``.
131 131
132 See also `ctrl-alt-del`_. 132 See also `ctrl-alt-del`_.
133 133
134 134
135 cap_last_cap 135 cap_last_cap
136 ============ 136 ============
137 137
138 Highest valid capability of the running kernel 138 Highest valid capability of the running kernel. Exports
139 ``CAP_LAST_CAP`` from the kernel. 139 ``CAP_LAST_CAP`` from the kernel.
140 140
141 141
142 .. _core_pattern: 142 .. _core_pattern:
143 143
144 core_pattern 144 core_pattern
145 ============ 145 ============
146 146
147 ``core_pattern`` is used to specify a core dum 147 ``core_pattern`` is used to specify a core dumpfile pattern name.
148 148
149 * max length 127 characters; default value is 149 * max length 127 characters; default value is "core"
150 * ``core_pattern`` is used as a pattern templa 150 * ``core_pattern`` is used as a pattern template for the output
151 filename; certain string patterns (beginning 151 filename; certain string patterns (beginning with '%') are
152 substituted with their actual values. 152 substituted with their actual values.
153 * backward compatibility with ``core_uses_pid` 153 * backward compatibility with ``core_uses_pid``:
154 154
155 If ``core_pattern`` does not include " 155 If ``core_pattern`` does not include "%p" (default does not)
156 and ``core_uses_pid`` is set, then .PI 156 and ``core_uses_pid`` is set, then .PID will be appended to
157 the filename. 157 the filename.
158 158
159 * corename format specifiers 159 * corename format specifiers
160 160
161 ======== ====================== 161 ======== ==========================================
162 %<NUL> '%' is dropped 162 %<NUL> '%' is dropped
163 %% output one '%' 163 %% output one '%'
164 %p pid 164 %p pid
165 %P global pid (init PID n 165 %P global pid (init PID namespace)
166 %i tid 166 %i tid
167 %I global tid (init PID n 167 %I global tid (init PID namespace)
168 %u uid (in initial user n 168 %u uid (in initial user namespace)
169 %g gid (in initial user n 169 %g gid (in initial user namespace)
170 %d dump mode, matches ``P 170 %d dump mode, matches ``PR_SET_DUMPABLE`` and
171 ``/proc/sys/fs/suid_du 171 ``/proc/sys/fs/suid_dumpable``
172 %s signal number 172 %s signal number
173 %t UNIX time of dump 173 %t UNIX time of dump
174 %h hostname 174 %h hostname
175 %e executable filename (m 175 %e executable filename (may be shortened, could be changed by prctl etc)
176 %f executable filename 176 %f executable filename
177 %E executable path 177 %E executable path
178 %c maximum size of core f 178 %c maximum size of core file by resource limit RLIMIT_CORE
179 %C CPU the task ran on 179 %C CPU the task ran on
180 %<OTHER> both are dropped 180 %<OTHER> both are dropped
181 ======== ====================== 181 ======== ==========================================
182 182
183 * If the first character of the pattern is a ' 183 * If the first character of the pattern is a '|', the kernel will treat
184 the rest of the pattern as a command to run. 184 the rest of the pattern as a command to run. The core dump will be
185 written to the standard input of that progra 185 written to the standard input of that program instead of to a file.
186 186
187 187
188 core_pipe_limit 188 core_pipe_limit
189 =============== 189 ===============
190 190
191 This sysctl is only applicable when `core_patt 191 This sysctl is only applicable when `core_pattern`_ is configured to
192 pipe core files to a user space helper (when t 192 pipe core files to a user space helper (when the first character of
193 ``core_pattern`` is a '|', see above). 193 ``core_pattern`` is a '|', see above).
194 When collecting cores via a pipe to an applica 194 When collecting cores via a pipe to an application, it is occasionally
195 useful for the collecting application to gathe 195 useful for the collecting application to gather data about the
196 crashing process from its ``/proc/pid`` direct 196 crashing process from its ``/proc/pid`` directory.
197 In order to do this safely, the kernel must wa 197 In order to do this safely, the kernel must wait for the collecting
198 process to exit, so as not to remove the crash 198 process to exit, so as not to remove the crashing processes proc files
199 prematurely. 199 prematurely.
200 This in turn creates the possibility that a mi 200 This in turn creates the possibility that a misbehaving userspace
201 collecting process can block the reaping of a 201 collecting process can block the reaping of a crashed process simply
202 by never exiting. 202 by never exiting.
203 This sysctl defends against that. 203 This sysctl defends against that.
204 It defines how many concurrent crashing proces 204 It defines how many concurrent crashing processes may be piped to user
205 space applications in parallel. 205 space applications in parallel.
206 If this value is exceeded, then those crashing 206 If this value is exceeded, then those crashing processes above that
207 value are noted via the kernel log and their c 207 value are noted via the kernel log and their cores are skipped.
208 0 is a special value, indicating that unlimite 208 0 is a special value, indicating that unlimited processes may be
209 captured in parallel, but that no waiting will 209 captured in parallel, but that no waiting will take place (i.e. the
210 collecting process is not guaranteed access to 210 collecting process is not guaranteed access to ``/proc/<crashing
211 pid>/``). 211 pid>/``).
212 This value defaults to 0. 212 This value defaults to 0.
213 213
214 214
215 core_uses_pid 215 core_uses_pid
216 ============= 216 =============
217 217
218 The default coredump filename is "core". By s 218 The default coredump filename is "core". By setting
219 ``core_uses_pid`` to 1, the coredump filename 219 ``core_uses_pid`` to 1, the coredump filename becomes core.PID.
220 If `core_pattern`_ does not include "%p" (defa 220 If `core_pattern`_ does not include "%p" (default does not)
221 and ``core_uses_pid`` is set, then .PID will b 221 and ``core_uses_pid`` is set, then .PID will be appended to
222 the filename. 222 the filename.
223 223
224 224
225 ctrl-alt-del 225 ctrl-alt-del
226 ============ 226 ============
227 227
228 When the value in this file is 0, ctrl-alt-del 228 When the value in this file is 0, ctrl-alt-del is trapped and
229 sent to the ``init(1)`` program to handle a gr 229 sent to the ``init(1)`` program to handle a graceful restart.
230 When, however, the value is > 0, Linux's react 230 When, however, the value is > 0, Linux's reaction to a Vulcan
231 Nerve Pinch (tm) will be an immediate reboot, 231 Nerve Pinch (tm) will be an immediate reboot, without even
232 syncing its dirty buffers. 232 syncing its dirty buffers.
233 233
234 Note: 234 Note:
235 when a program (like dosemu) has the keyboar 235 when a program (like dosemu) has the keyboard in 'raw'
236 mode, the ctrl-alt-del is intercepted by the 236 mode, the ctrl-alt-del is intercepted by the program before it
237 ever reaches the kernel tty layer, and it's 237 ever reaches the kernel tty layer, and it's up to the program
238 to decide what to do with it. 238 to decide what to do with it.
239 239
240 240
241 dmesg_restrict 241 dmesg_restrict
242 ============== 242 ==============
243 243
244 This toggle indicates whether unprivileged use 244 This toggle indicates whether unprivileged users are prevented
245 from using ``dmesg(8)`` to view messages from 245 from using ``dmesg(8)`` to view messages from the kernel's log
246 buffer. 246 buffer.
247 When ``dmesg_restrict`` is set to 0 there are 247 When ``dmesg_restrict`` is set to 0 there are no restrictions.
248 When ``dmesg_restrict`` is set to 1, users mus 248 When ``dmesg_restrict`` is set to 1, users must have
249 ``CAP_SYSLOG`` to use ``dmesg(8)``. 249 ``CAP_SYSLOG`` to use ``dmesg(8)``.
250 250
251 The kernel config option ``CONFIG_SECURITY_DME 251 The kernel config option ``CONFIG_SECURITY_DMESG_RESTRICT`` sets the
252 default value of ``dmesg_restrict``. 252 default value of ``dmesg_restrict``.
253 253
254 254
255 domainname & hostname 255 domainname & hostname
256 ===================== 256 =====================
257 257
258 These files can be used to set the NIS/YP doma 258 These files can be used to set the NIS/YP domainname and the
259 hostname of your box in exactly the same way a 259 hostname of your box in exactly the same way as the commands
260 domainname and hostname, i.e.:: 260 domainname and hostname, i.e.::
261 261
262 # echo "darkstar" > /proc/sys/kernel/h 262 # echo "darkstar" > /proc/sys/kernel/hostname
263 # echo "mydomain" > /proc/sys/kernel/d 263 # echo "mydomain" > /proc/sys/kernel/domainname
264 264
265 has the same effect as:: 265 has the same effect as::
266 266
267 # hostname "darkstar" 267 # hostname "darkstar"
268 # domainname "mydomain" 268 # domainname "mydomain"
269 269
270 Note, however, that the classic darkstar.frop. 270 Note, however, that the classic darkstar.frop.org has the
271 hostname "darkstar" and DNS (Internet Domain N 271 hostname "darkstar" and DNS (Internet Domain Name Server)
272 domainname "frop.org", not to be confused with 272 domainname "frop.org", not to be confused with the NIS (Network
273 Information Service) or YP (Yellow Pages) doma 273 Information Service) or YP (Yellow Pages) domainname. These two
274 domain names are in general different. For a d 274 domain names are in general different. For a detailed discussion
275 see the ``hostname(1)`` man page. 275 see the ``hostname(1)`` man page.
276 276
277 277
278 firmware_config 278 firmware_config
279 =============== 279 ===============
280 280
281 See Documentation/driver-api/firmware/fallback 281 See Documentation/driver-api/firmware/fallback-mechanisms.rst.
282 282
283 The entries in this directory allow the firmwa 283 The entries in this directory allow the firmware loader helper
284 fallback to be controlled: 284 fallback to be controlled:
285 285
286 * ``force_sysfs_fallback``, when set to 1, for 286 * ``force_sysfs_fallback``, when set to 1, forces the use of the
287 fallback; 287 fallback;
288 * ``ignore_sysfs_fallback``, when set to 1, ig 288 * ``ignore_sysfs_fallback``, when set to 1, ignores any fallback.
289 289
290 290
291 ftrace_dump_on_oops 291 ftrace_dump_on_oops
292 =================== 292 ===================
293 293
294 Determines whether ``ftrace_dump()`` should be 294 Determines whether ``ftrace_dump()`` should be called on an oops (or
295 kernel panic). This will output the contents o 295 kernel panic). This will output the contents of the ftrace buffers to
296 the console. This is very useful for capturin 296 the console. This is very useful for capturing traces that lead to
297 crashes and outputting them to a serial consol 297 crashes and outputting them to a serial console.
298 298
299 ======================= ====================== 299 ======================= ===========================================
300 0 Disabled (default). 300 0 Disabled (default).
301 1 Dump buffers of all CP 301 1 Dump buffers of all CPUs.
302 2(orig_cpu) Dump the buffer of the 302 2(orig_cpu) Dump the buffer of the CPU that triggered the
303 oops. 303 oops.
304 <instance> Dump the specific inst 304 <instance> Dump the specific instance buffer on all CPUs.
305 <instance>=2(orig_cpu) Dump the specific inst 305 <instance>=2(orig_cpu) Dump the specific instance buffer on the CPU
306 that triggered the oop 306 that triggered the oops.
307 ======================= ====================== 307 ======================= ===========================================
308 308
309 Multiple instance dump is also supported, and 309 Multiple instance dump is also supported, and instances are separated
310 by commas. If global buffer also needs to be d 310 by commas. If global buffer also needs to be dumped, please specify
311 the dump mode (1/2/orig_cpu) first for global 311 the dump mode (1/2/orig_cpu) first for global buffer.
312 312
313 So for example to dump "foo" and "bar" instanc 313 So for example to dump "foo" and "bar" instance buffer on all CPUs,
314 user can:: 314 user can::
315 315
316 echo "foo,bar" > /proc/sys/kernel/ftrace_dum 316 echo "foo,bar" > /proc/sys/kernel/ftrace_dump_on_oops
317 317
318 To dump global buffer and "foo" instance buffe 318 To dump global buffer and "foo" instance buffer on all
319 CPUs along with the "bar" instance buffer on C 319 CPUs along with the "bar" instance buffer on CPU that triggered the
320 oops, user can:: 320 oops, user can::
321 321
322 echo "1,foo,bar=2" > /proc/sys/kernel/ftrace 322 echo "1,foo,bar=2" > /proc/sys/kernel/ftrace_dump_on_oops
323 323
324 ftrace_enabled, stack_tracer_enabled 324 ftrace_enabled, stack_tracer_enabled
325 ==================================== 325 ====================================
326 326
327 See Documentation/trace/ftrace.rst. 327 See Documentation/trace/ftrace.rst.
328 328
329 329
330 hardlockup_all_cpu_backtrace 330 hardlockup_all_cpu_backtrace
331 ============================ 331 ============================
332 332
333 This value controls the hard lockup detector b 333 This value controls the hard lockup detector behavior when a hard
334 lockup condition is detected as to whether or 334 lockup condition is detected as to whether or not to gather further
335 debug information. If enabled, arch-specific a 335 debug information. If enabled, arch-specific all-CPU stack dumping
336 will be initiated. 336 will be initiated.
337 337
338 = ============================================ 338 = ============================================
339 0 Do nothing. This is the default behavior. 339 0 Do nothing. This is the default behavior.
340 1 On detection capture more debug information. 340 1 On detection capture more debug information.
341 = ============================================ 341 = ============================================
342 342
343 343
344 hardlockup_panic 344 hardlockup_panic
345 ================ 345 ================
346 346
347 This parameter can be used to control whether 347 This parameter can be used to control whether the kernel panics
348 when a hard lockup is detected. 348 when a hard lockup is detected.
349 349
350 = =========================== 350 = ===========================
351 0 Don't panic on hard lockup. 351 0 Don't panic on hard lockup.
352 1 Panic on hard lockup. 352 1 Panic on hard lockup.
353 = =========================== 353 = ===========================
354 354
355 See Documentation/admin-guide/lockup-watchdogs 355 See Documentation/admin-guide/lockup-watchdogs.rst for more information.
356 This can also be set using the nmi_watchdog ke 356 This can also be set using the nmi_watchdog kernel parameter.
357 357
358 358
359 hotplug 359 hotplug
360 ======= 360 =======
361 361
362 Path for the hotplug policy agent. 362 Path for the hotplug policy agent.
363 Default value is ``CONFIG_UEVENT_HELPER_PATH`` 363 Default value is ``CONFIG_UEVENT_HELPER_PATH``, which in turn defaults
364 to the empty string. 364 to the empty string.
365 365
366 This file only exists when ``CONFIG_UEVENT_HEL 366 This file only exists when ``CONFIG_UEVENT_HELPER`` is enabled. Most
367 modern systems rely exclusively on the netlink 367 modern systems rely exclusively on the netlink-based uevent source and
368 don't need this. 368 don't need this.
369 369
370 370
371 hung_task_all_cpu_backtrace 371 hung_task_all_cpu_backtrace
372 =========================== 372 ===========================
373 373
374 If this option is set, the kernel will send an 374 If this option is set, the kernel will send an NMI to all CPUs to dump
375 their backtraces when a hung task is detected. 375 their backtraces when a hung task is detected. This file shows up if
376 CONFIG_DETECT_HUNG_TASK and CONFIG_SMP are ena 376 CONFIG_DETECT_HUNG_TASK and CONFIG_SMP are enabled.
377 377
378 0: Won't show all CPUs backtraces when a hung 378 0: Won't show all CPUs backtraces when a hung task is detected.
379 This is the default behavior. 379 This is the default behavior.
380 380
381 1: Will non-maskably interrupt all CPUs and du 381 1: Will non-maskably interrupt all CPUs and dump their backtraces when
382 a hung task is detected. 382 a hung task is detected.
383 383
384 384
385 hung_task_panic 385 hung_task_panic
386 =============== 386 ===============
387 387
388 Controls the kernel's behavior when a hung tas 388 Controls the kernel's behavior when a hung task is detected.
389 This file shows up if ``CONFIG_DETECT_HUNG_TAS 389 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
390 390
391 = ============================================ 391 = =================================================
392 0 Continue operation. This is the default beha 392 0 Continue operation. This is the default behavior.
393 1 Panic immediately. 393 1 Panic immediately.
394 = ============================================ 394 = =================================================
395 395
396 396
397 hung_task_check_count 397 hung_task_check_count
398 ===================== 398 =====================
399 399
400 The upper bound on the number of tasks that ar 400 The upper bound on the number of tasks that are checked.
401 This file shows up if ``CONFIG_DETECT_HUNG_TAS 401 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
402 402
403 403
404 hung_task_timeout_secs 404 hung_task_timeout_secs
405 ====================== 405 ======================
406 406
407 When a task in D state did not get scheduled 407 When a task in D state did not get scheduled
408 for more than this value report a warning. 408 for more than this value report a warning.
409 This file shows up if ``CONFIG_DETECT_HUNG_TAS 409 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
410 410
411 0 means infinite timeout, no checking is done. 411 0 means infinite timeout, no checking is done.
412 412
413 Possible values to set are in range {0:``LONG_ 413 Possible values to set are in range {0:``LONG_MAX``/``HZ``}.
414 414
415 415
416 hung_task_check_interval_secs 416 hung_task_check_interval_secs
417 ============================= 417 =============================
418 418
419 Hung task check interval. If hung task checkin 419 Hung task check interval. If hung task checking is enabled
420 (see `hung_task_timeout_secs`_), the check is 420 (see `hung_task_timeout_secs`_), the check is done every
421 ``hung_task_check_interval_secs`` seconds. 421 ``hung_task_check_interval_secs`` seconds.
422 This file shows up if ``CONFIG_DETECT_HUNG_TAS 422 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
423 423
424 0 (default) means use ``hung_task_timeout_secs 424 0 (default) means use ``hung_task_timeout_secs`` as checking
425 interval. 425 interval.
426 426
427 Possible values to set are in range {0:``LONG_ 427 Possible values to set are in range {0:``LONG_MAX``/``HZ``}.
428 428
429 429
430 hung_task_warnings 430 hung_task_warnings
431 ================== 431 ==================
432 432
433 The maximum number of warnings to report. Duri 433 The maximum number of warnings to report. During a check interval
434 if a hung task is detected, this value is decr 434 if a hung task is detected, this value is decreased by 1.
435 When this value reaches 0, no more warnings wi 435 When this value reaches 0, no more warnings will be reported.
436 This file shows up if ``CONFIG_DETECT_HUNG_TAS 436 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
437 437
438 -1: report an infinite number of warnings. 438 -1: report an infinite number of warnings.
439 439
440 440
441 hyperv_record_panic_msg 441 hyperv_record_panic_msg
442 ======================= 442 =======================
443 443
444 Controls whether the panic kmsg data should be 444 Controls whether the panic kmsg data should be reported to Hyper-V.
445 445
446 = ============================================ 446 = =========================================================
447 0 Do not report panic kmsg data. 447 0 Do not report panic kmsg data.
448 1 Report the panic kmsg data. This is the defa 448 1 Report the panic kmsg data. This is the default behavior.
449 = ============================================ 449 = =========================================================
450 450
451 451
452 ignore-unaligned-usertrap 452 ignore-unaligned-usertrap
453 ========================= 453 =========================
454 454
455 On architectures where unaligned accesses caus 455 On architectures where unaligned accesses cause traps, and where this
456 feature is supported (``CONFIG_SYSCTL_ARCH_UNA 456 feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_NO_WARN``;
457 currently, ``arc``, ``parisc`` and ``loongarch 457 currently, ``arc``, ``parisc`` and ``loongarch``), controls whether all
458 unaligned traps are logged. 458 unaligned traps are logged.
459 459
460 = ============================================ 460 = =============================================================
461 0 Log all unaligned accesses. 461 0 Log all unaligned accesses.
462 1 Only warn the first time a process traps. Th 462 1 Only warn the first time a process traps. This is the default
463 setting. 463 setting.
464 = ============================================ 464 = =============================================================
465 465
466 See also `unaligned-trap`_. 466 See also `unaligned-trap`_.
467 467
468 io_uring_disabled 468 io_uring_disabled
469 ================= 469 =================
470 470
471 Prevents all processes from creating new io_ur 471 Prevents all processes from creating new io_uring instances. Enabling this
472 shrinks the kernel's attack surface. 472 shrinks the kernel's attack surface.
473 473
474 = ============================================ 474 = ======================================================================
475 0 All processes can create io_uring instances 475 0 All processes can create io_uring instances as normal. This is the
476 default setting. 476 default setting.
477 1 io_uring creation is disabled (io_uring_setu 477 1 io_uring creation is disabled (io_uring_setup() will fail with
478 -EPERM) for unprivileged processes not in th 478 -EPERM) for unprivileged processes not in the io_uring_group group.
479 Existing io_uring instances can still be use 479 Existing io_uring instances can still be used. See the
480 documentation for io_uring_group for more in 480 documentation for io_uring_group for more information.
481 2 io_uring creation is disabled for all proces 481 2 io_uring creation is disabled for all processes. io_uring_setup()
482 always fails with -EPERM. Existing io_uring 482 always fails with -EPERM. Existing io_uring instances can still be
483 used. 483 used.
484 = ============================================ 484 = ======================================================================
485 485
486 486
487 io_uring_group 487 io_uring_group
488 ============== 488 ==============
489 489
490 When io_uring_disabled is set to 1, a process 490 When io_uring_disabled is set to 1, a process must either be
491 privileged (CAP_SYS_ADMIN) or be in the io_uri 491 privileged (CAP_SYS_ADMIN) or be in the io_uring_group group in order
492 to create an io_uring instance. If io_uring_g 492 to create an io_uring instance. If io_uring_group is set to -1 (the
493 default), only processes with the CAP_SYS_ADMI 493 default), only processes with the CAP_SYS_ADMIN capability may create
494 io_uring instances. 494 io_uring instances.
495 495
496 496
497 kexec_load_disabled 497 kexec_load_disabled
498 =================== 498 ===================
499 499
500 A toggle indicating if the syscalls ``kexec_lo 500 A toggle indicating if the syscalls ``kexec_load`` and
501 ``kexec_file_load`` have been disabled. 501 ``kexec_file_load`` have been disabled.
502 This value defaults to 0 (false: ``kexec_*load 502 This value defaults to 0 (false: ``kexec_*load`` enabled), but can be
503 set to 1 (true: ``kexec_*load`` disabled). 503 set to 1 (true: ``kexec_*load`` disabled).
504 Once true, kexec can no longer be used, and th 504 Once true, kexec can no longer be used, and the toggle cannot be set
505 back to false. 505 back to false.
506 This allows a kexec image to be loaded before 506 This allows a kexec image to be loaded before disabling the syscall,
507 allowing a system to set up (and later use) an 507 allowing a system to set up (and later use) an image without it being
508 altered. 508 altered.
509 Generally used together with the `modules_disa 509 Generally used together with the `modules_disabled`_ sysctl.
510 510
511 kexec_load_limit_panic 511 kexec_load_limit_panic
512 ====================== 512 ======================
513 513
514 This parameter specifies a limit to the number 514 This parameter specifies a limit to the number of times the syscalls
515 ``kexec_load`` and ``kexec_file_load`` can be 515 ``kexec_load`` and ``kexec_file_load`` can be called with a crash
516 image. It can only be set with a more restrict 516 image. It can only be set with a more restrictive value than the
517 current one. 517 current one.
518 518
519 == =========================================== 519 == ======================================================
520 -1 Unlimited calls to kexec. This is the defau 520 -1 Unlimited calls to kexec. This is the default setting.
521 N Number of calls left. 521 N Number of calls left.
522 == =========================================== 522 == ======================================================
523 523
524 kexec_load_limit_reboot 524 kexec_load_limit_reboot
525 ======================= 525 =======================
526 526
527 Similar functionality as ``kexec_load_limit_pa 527 Similar functionality as ``kexec_load_limit_panic``, but for a normal
528 image. 528 image.
529 529
530 kptr_restrict 530 kptr_restrict
531 ============= 531 =============
532 532
533 This toggle indicates whether restrictions are 533 This toggle indicates whether restrictions are placed on
534 exposing kernel addresses via ``/proc`` and ot 534 exposing kernel addresses via ``/proc`` and other interfaces.
535 535
536 When ``kptr_restrict`` is set to 0 (the defaul 536 When ``kptr_restrict`` is set to 0 (the default) the address is hashed
537 before printing. 537 before printing.
538 (This is the equivalent to %p.) 538 (This is the equivalent to %p.)
539 539
540 When ``kptr_restrict`` is set to 1, kernel poi 540 When ``kptr_restrict`` is set to 1, kernel pointers printed using the
541 %pK format specifier will be replaced with 0s 541 %pK format specifier will be replaced with 0s unless the user has
542 ``CAP_SYSLOG`` and effective user and group id 542 ``CAP_SYSLOG`` and effective user and group ids are equal to the real
543 ids. 543 ids.
544 This is because %pK checks are done at read() 544 This is because %pK checks are done at read() time rather than open()
545 time, so if permissions are elevated between t 545 time, so if permissions are elevated between the open() and the read()
546 (e.g via a setuid binary) then %pK will not le 546 (e.g via a setuid binary) then %pK will not leak kernel pointers to
547 unprivileged users. 547 unprivileged users.
548 Note, this is a temporary solution only. 548 Note, this is a temporary solution only.
549 The correct long-term solution is to do the pe 549 The correct long-term solution is to do the permission checks at
550 open() time. 550 open() time.
551 Consider removing world read permissions from 551 Consider removing world read permissions from files that use %pK, and
552 using `dmesg_restrict`_ to protect against use 552 using `dmesg_restrict`_ to protect against uses of %pK in ``dmesg(8)``
553 if leaking kernel pointer values to unprivileg 553 if leaking kernel pointer values to unprivileged users is a concern.
554 554
555 When ``kptr_restrict`` is set to 2, kernel poi 555 When ``kptr_restrict`` is set to 2, kernel pointers printed using
556 %pK will be replaced with 0s regardless of pri 556 %pK will be replaced with 0s regardless of privileges.
557 557
558 558
559 modprobe 559 modprobe
560 ======== 560 ========
561 561
562 The full path to the usermode helper for autol 562 The full path to the usermode helper for autoloading kernel modules,
563 by default ``CONFIG_MODPROBE_PATH``, which in 563 by default ``CONFIG_MODPROBE_PATH``, which in turn defaults to
564 "/sbin/modprobe". This binary is executed whe 564 "/sbin/modprobe". This binary is executed when the kernel requests a
565 module. For example, if userspace passes an u 565 module. For example, if userspace passes an unknown filesystem type
566 to mount(), then the kernel will automatically 566 to mount(), then the kernel will automatically request the
567 corresponding filesystem module by executing t 567 corresponding filesystem module by executing this usermode helper.
568 This usermode helper should insert the needed 568 This usermode helper should insert the needed module into the kernel.
569 569
570 This sysctl only affects module autoloading. 570 This sysctl only affects module autoloading. It has no effect on the
571 ability to explicitly insert modules. 571 ability to explicitly insert modules.
572 572
573 This sysctl can be used to debug module loadin 573 This sysctl can be used to debug module loading requests::
574 574
575 echo '#! /bin/sh' > /tmp/modprobe 575 echo '#! /bin/sh' > /tmp/modprobe
576 echo 'echo "$@" >> /tmp/modprobe.log' >> / 576 echo 'echo "$@" >> /tmp/modprobe.log' >> /tmp/modprobe
577 echo 'exec /sbin/modprobe "$@"' >> /tmp/mo 577 echo 'exec /sbin/modprobe "$@"' >> /tmp/modprobe
578 chmod a+x /tmp/modprobe 578 chmod a+x /tmp/modprobe
579 echo /tmp/modprobe > /proc/sys/kernel/modp 579 echo /tmp/modprobe > /proc/sys/kernel/modprobe
580 580
581 Alternatively, if this sysctl is set to the em 581 Alternatively, if this sysctl is set to the empty string, then module
582 autoloading is completely disabled. The kerne 582 autoloading is completely disabled. The kernel will not try to
583 execute a usermode helper at all, nor will it 583 execute a usermode helper at all, nor will it call the
584 kernel_module_request LSM hook. 584 kernel_module_request LSM hook.
585 585
586 If CONFIG_STATIC_USERMODEHELPER=y is set in th 586 If CONFIG_STATIC_USERMODEHELPER=y is set in the kernel configuration,
587 then the configured static usermode helper ove 587 then the configured static usermode helper overrides this sysctl,
588 except that the empty string is still accepted 588 except that the empty string is still accepted to completely disable
589 module autoloading as described above. 589 module autoloading as described above.
590 590
591 modules_disabled 591 modules_disabled
592 ================ 592 ================
593 593
594 A toggle value indicating if modules are allow 594 A toggle value indicating if modules are allowed to be loaded
595 in an otherwise modular kernel. This toggle d 595 in an otherwise modular kernel. This toggle defaults to off
596 (0), but can be set true (1). Once true, modu 596 (0), but can be set true (1). Once true, modules can be
597 neither loaded nor unloaded, and the toggle ca 597 neither loaded nor unloaded, and the toggle cannot be set back
598 to false. Generally used with the `kexec_load 598 to false. Generally used with the `kexec_load_disabled`_ toggle.
599 599
600 600
601 .. _msgmni: 601 .. _msgmni:
602 602
603 msgmax, msgmnb, and msgmni 603 msgmax, msgmnb, and msgmni
604 ========================== 604 ==========================
605 605
606 ``msgmax`` is the maximum size of an IPC messa 606 ``msgmax`` is the maximum size of an IPC message, in bytes. 8192 by
607 default (``MSGMAX``). 607 default (``MSGMAX``).
608 608
609 ``msgmnb`` is the maximum size of an IPC queue 609 ``msgmnb`` is the maximum size of an IPC queue, in bytes. 16384 by
610 default (``MSGMNB``). 610 default (``MSGMNB``).
611 611
612 ``msgmni`` is the maximum number of IPC queues 612 ``msgmni`` is the maximum number of IPC queues. 32000 by default
613 (``MSGMNI``). 613 (``MSGMNI``).
614 614
615 All of these parameters are set per ipc namesp 615 All of these parameters are set per ipc namespace. The maximum number of bytes
616 in POSIX message queues is limited by ``RLIMIT 616 in POSIX message queues is limited by ``RLIMIT_MSGQUEUE``. This limit is
617 respected hierarchically in the each user name 617 respected hierarchically in the each user namespace.
618 618
619 msg_next_id, sem_next_id, and shm_next_id (Sys 619 msg_next_id, sem_next_id, and shm_next_id (System V IPC)
620 ============================================== 620 ========================================================
621 621
622 These three toggles allows to specify desired 622 These three toggles allows to specify desired id for next allocated IPC
623 object: message, semaphore or shared memory re 623 object: message, semaphore or shared memory respectively.
624 624
625 By default they are equal to -1, which means g 625 By default they are equal to -1, which means generic allocation logic.
626 Possible values to set are in range {0:``INT_M 626 Possible values to set are in range {0:``INT_MAX``}.
627 627
628 Notes: 628 Notes:
629 1) kernel doesn't guarantee, that new object 629 1) kernel doesn't guarantee, that new object will have desired id. So,
630 it's up to userspace, how to handle an ob 630 it's up to userspace, how to handle an object with "wrong" id.
631 2) Toggle with non-default value will be set 631 2) Toggle with non-default value will be set back to -1 by kernel after
632 successful IPC object allocation. If an I 632 successful IPC object allocation. If an IPC object allocation syscall
633 fails, it is undefined if the value remai 633 fails, it is undefined if the value remains unmodified or is reset to -1.
634 634
635 635
636 ngroups_max 636 ngroups_max
637 =========== 637 ===========
638 638
639 Maximum number of supplementary groups, _i.e._ 639 Maximum number of supplementary groups, _i.e._ the maximum size which
640 ``setgroups`` will accept. Exports ``NGROUPS_M 640 ``setgroups`` will accept. Exports ``NGROUPS_MAX`` from the kernel.
641 641
642 642
643 643
644 nmi_watchdog 644 nmi_watchdog
645 ============ 645 ============
646 646
647 This parameter can be used to control the NMI 647 This parameter can be used to control the NMI watchdog
648 (i.e. the hard lockup detector) on x86 systems 648 (i.e. the hard lockup detector) on x86 systems.
649 649
650 = ================================= 650 = =================================
651 0 Disable the hard lockup detector. 651 0 Disable the hard lockup detector.
652 1 Enable the hard lockup detector. 652 1 Enable the hard lockup detector.
653 = ================================= 653 = =================================
654 654
655 The hard lockup detector monitors each CPU for 655 The hard lockup detector monitors each CPU for its ability to respond to
656 timer interrupts. The mechanism utilizes CPU p 656 timer interrupts. The mechanism utilizes CPU performance counter registers
657 that are programmed to generate Non-Maskable I 657 that are programmed to generate Non-Maskable Interrupts (NMIs) periodically
658 while a CPU is busy. Hence, the alternative na 658 while a CPU is busy. Hence, the alternative name 'NMI watchdog'.
659 659
660 The NMI watchdog is disabled by default if the 660 The NMI watchdog is disabled by default if the kernel is running as a guest
661 in a KVM virtual machine. This default can be 661 in a KVM virtual machine. This default can be overridden by adding::
662 662
663 nmi_watchdog=1 663 nmi_watchdog=1
664 664
665 to the guest kernel command line (see 665 to the guest kernel command line (see
666 Documentation/admin-guide/kernel-parameters.rs 666 Documentation/admin-guide/kernel-parameters.rst).
667 667
668 668
669 nmi_wd_lpm_factor (PPC only) 669 nmi_wd_lpm_factor (PPC only)
670 ============================ 670 ============================
671 671
672 Factor to apply to the NMI watchdog timeout (o 672 Factor to apply to the NMI watchdog timeout (only when ``nmi_watchdog`` is
673 set to 1). This factor represents the percenta 673 set to 1). This factor represents the percentage added to
674 ``watchdog_thresh`` when calculating the NMI w 674 ``watchdog_thresh`` when calculating the NMI watchdog timeout during an
675 LPM. The soft lockup timeout is not impacted. 675 LPM. The soft lockup timeout is not impacted.
676 676
677 A value of 0 means no change. The default valu 677 A value of 0 means no change. The default value is 200 meaning the NMI
678 watchdog is set to 30s (based on ``watchdog_th 678 watchdog is set to 30s (based on ``watchdog_thresh`` equal to 10).
679 679
680 680
681 numa_balancing 681 numa_balancing
682 ============== 682 ==============
683 683
684 Enables/disables and configures automatic page 684 Enables/disables and configures automatic page fault based NUMA memory
685 balancing. Memory is moved automatically to n 685 balancing. Memory is moved automatically to nodes that access it often.
686 The value to set can be the result of ORing th 686 The value to set can be the result of ORing the following:
687 687
688 = ================================= 688 = =================================
689 0 NUMA_BALANCING_DISABLED 689 0 NUMA_BALANCING_DISABLED
690 1 NUMA_BALANCING_NORMAL 690 1 NUMA_BALANCING_NORMAL
691 2 NUMA_BALANCING_MEMORY_TIERING 691 2 NUMA_BALANCING_MEMORY_TIERING
692 = ================================= 692 = =================================
693 693
694 Or NUMA_BALANCING_NORMAL to optimize page plac 694 Or NUMA_BALANCING_NORMAL to optimize page placement among different
695 NUMA nodes to reduce remote accessing. On NUM 695 NUMA nodes to reduce remote accessing. On NUMA machines, there is a
696 performance penalty if remote memory is access 696 performance penalty if remote memory is accessed by a CPU. When this
697 feature is enabled the kernel samples what tas 697 feature is enabled the kernel samples what task thread is accessing
698 memory by periodically unmapping pages and lat 698 memory by periodically unmapping pages and later trapping a page
699 fault. At the time of the page fault, it is de 699 fault. At the time of the page fault, it is determined if the data
700 being accessed should be migrated to a local m 700 being accessed should be migrated to a local memory node.
701 701
702 The unmapping of pages and trapping faults inc 702 The unmapping of pages and trapping faults incur additional overhead that
703 ideally is offset by improved memory locality 703 ideally is offset by improved memory locality but there is no universal
704 guarantee. If the target workload is already b 704 guarantee. If the target workload is already bound to NUMA nodes then this
705 feature should be disabled. 705 feature should be disabled.
706 706
707 Or NUMA_BALANCING_MEMORY_TIERING to optimize p 707 Or NUMA_BALANCING_MEMORY_TIERING to optimize page placement among
708 different types of memory (represented as diff 708 different types of memory (represented as different NUMA nodes) to
709 place the hot pages in the fast memory. This 709 place the hot pages in the fast memory. This is implemented based on
710 unmapping and page fault too. 710 unmapping and page fault too.
711 711
712 numa_balancing_promote_rate_limit_MBps 712 numa_balancing_promote_rate_limit_MBps
713 ====================================== 713 ======================================
714 714
715 Too high promotion/demotion throughput between 715 Too high promotion/demotion throughput between different memory types
716 may hurt application latency. This can be use 716 may hurt application latency. This can be used to rate limit the
717 promotion throughput. The per-node max promot 717 promotion throughput. The per-node max promotion throughput in MB/s
718 will be limited to be no more than the set val 718 will be limited to be no more than the set value.
719 719
720 A rule of thumb is to set this to less than 1/ 720 A rule of thumb is to set this to less than 1/10 of the PMEM node
721 write bandwidth. 721 write bandwidth.
722 722
723 oops_all_cpu_backtrace 723 oops_all_cpu_backtrace
724 ====================== 724 ======================
725 725
726 If this option is set, the kernel will send an 726 If this option is set, the kernel will send an NMI to all CPUs to dump
727 their backtraces when an oops event occurs. It 727 their backtraces when an oops event occurs. It should be used as a last
728 resort in case a panic cannot be triggered (to 728 resort in case a panic cannot be triggered (to protect VMs running, for
729 example) or kdump can't be collected. This fil 729 example) or kdump can't be collected. This file shows up if CONFIG_SMP
730 is enabled. 730 is enabled.
731 731
732 0: Won't show all CPUs backtraces when an oops 732 0: Won't show all CPUs backtraces when an oops is detected.
733 This is the default behavior. 733 This is the default behavior.
734 734
735 1: Will non-maskably interrupt all CPUs and du 735 1: Will non-maskably interrupt all CPUs and dump their backtraces when
736 an oops event is detected. 736 an oops event is detected.
737 737
738 738
739 oops_limit 739 oops_limit
740 ========== 740 ==========
741 741
742 Number of kernel oopses after which the kernel 742 Number of kernel oopses after which the kernel should panic when
743 ``panic_on_oops`` is not set. Setting this to 743 ``panic_on_oops`` is not set. Setting this to 0 disables checking
744 the count. Setting this to 1 has the same eff 744 the count. Setting this to 1 has the same effect as setting
745 ``panic_on_oops=1``. The default value is 1000 745 ``panic_on_oops=1``. The default value is 10000.
746 746
747 747
748 osrelease, ostype & version 748 osrelease, ostype & version
749 =========================== 749 ===========================
750 750
751 :: 751 ::
752 752
753 # cat osrelease 753 # cat osrelease
754 2.1.88 754 2.1.88
755 # cat ostype 755 # cat ostype
756 Linux 756 Linux
757 # cat version 757 # cat version
758 #5 Wed Feb 25 21:49:24 MET 1998 758 #5 Wed Feb 25 21:49:24 MET 1998
759 759
760 The files ``osrelease`` and ``ostype`` should 760 The files ``osrelease`` and ``ostype`` should be clear enough.
761 ``version`` 761 ``version``
762 needs a little more clarification however. The 762 needs a little more clarification however. The '#5' means that
763 this is the fifth kernel built from this sourc 763 this is the fifth kernel built from this source base and the
764 date behind it indicates the time the kernel w 764 date behind it indicates the time the kernel was built.
765 The only way to tune these values is to rebuil 765 The only way to tune these values is to rebuild the kernel :-)
766 766
767 767
768 overflowgid & overflowuid 768 overflowgid & overflowuid
769 ========================= 769 =========================
770 770
771 if your architecture did not always support 32 771 if your architecture did not always support 32-bit UIDs (i.e. arm,
772 i386, m68k, sh, and sparc32), a fixed UID and 772 i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to
773 applications that use the old 16-bit UID/GID s 773 applications that use the old 16-bit UID/GID system calls, if the
774 actual UID or GID would exceed 65535. 774 actual UID or GID would exceed 65535.
775 775
776 These sysctls allow you to change the value of 776 These sysctls allow you to change the value of the fixed UID and GID.
777 The default is 65534. 777 The default is 65534.
778 778
779 779
780 panic 780 panic
781 ===== 781 =====
782 782
783 The value in this file determines the behaviou 783 The value in this file determines the behaviour of the kernel on a
784 panic: 784 panic:
785 785
786 * if zero, the kernel will loop forever; 786 * if zero, the kernel will loop forever;
787 * if negative, the kernel will reboot immediat 787 * if negative, the kernel will reboot immediately;
788 * if positive, the kernel will reboot after th 788 * if positive, the kernel will reboot after the corresponding number
789 of seconds. 789 of seconds.
790 790
791 When you use the software watchdog, the recomm 791 When you use the software watchdog, the recommended setting is 60.
792 792
793 793
794 panic_on_io_nmi 794 panic_on_io_nmi
795 =============== 795 ===============
796 796
797 Controls the kernel's behavior when a CPU rece 797 Controls the kernel's behavior when a CPU receives an NMI caused by
798 an IO error. 798 an IO error.
799 799
800 = ============================================ 800 = ==================================================================
801 0 Try to continue operation (default). 801 0 Try to continue operation (default).
802 1 Panic immediately. The IO error triggered an 802 1 Panic immediately. The IO error triggered an NMI. This indicates a
803 serious system condition which could result 803 serious system condition which could result in IO data corruption.
804 Rather than continuing, panicking might be a 804 Rather than continuing, panicking might be a better choice. Some
805 servers issue this sort of NMI when the dump 805 servers issue this sort of NMI when the dump button is pushed,
806 and you can use this option to take a crash 806 and you can use this option to take a crash dump.
807 = ============================================ 807 = ==================================================================
808 808
809 809
810 panic_on_oops 810 panic_on_oops
811 ============= 811 =============
812 812
813 Controls the kernel's behaviour when an oops o 813 Controls the kernel's behaviour when an oops or BUG is encountered.
814 814
815 = ============================================ 815 = ===================================================================
816 0 Try to continue operation. 816 0 Try to continue operation.
817 1 Panic immediately. If the `panic` sysctl is 817 1 Panic immediately. If the `panic` sysctl is also non-zero then the
818 machine will be rebooted. 818 machine will be rebooted.
819 = ============================================ 819 = ===================================================================
820 820
821 821
822 panic_on_stackoverflow 822 panic_on_stackoverflow
823 ====================== 823 ======================
824 824
825 Controls the kernel's behavior when detecting 825 Controls the kernel's behavior when detecting the overflows of
826 kernel, IRQ and exception stacks except a user 826 kernel, IRQ and exception stacks except a user stack.
827 This file shows up if ``CONFIG_DEBUG_STACKOVER 827 This file shows up if ``CONFIG_DEBUG_STACKOVERFLOW`` is enabled.
828 828
829 = ========================== 829 = ==========================
830 0 Try to continue operation. 830 0 Try to continue operation.
831 1 Panic immediately. 831 1 Panic immediately.
832 = ========================== 832 = ==========================
833 833
834 834
835 panic_on_unrecovered_nmi 835 panic_on_unrecovered_nmi
836 ======================== 836 ========================
837 837
838 The default Linux behaviour on an NMI of eithe 838 The default Linux behaviour on an NMI of either memory or unknown is
839 to continue operation. For many environments s 839 to continue operation. For many environments such as scientific
840 computing it is preferable that the box is tak 840 computing it is preferable that the box is taken out and the error
841 dealt with than an uncorrected parity/ECC erro 841 dealt with than an uncorrected parity/ECC error get propagated.
842 842
843 A small number of systems do generate NMIs for 843 A small number of systems do generate NMIs for bizarre random reasons
844 such as power management so the default is off 844 such as power management so the default is off. That sysctl works like
845 the existing panic controls already in that di 845 the existing panic controls already in that directory.
846 846
847 847
848 panic_on_warn 848 panic_on_warn
849 ============= 849 =============
850 850
851 Calls panic() in the WARN() path when set to 1 851 Calls panic() in the WARN() path when set to 1. This is useful to avoid
852 a kernel rebuild when attempting to kdump at t 852 a kernel rebuild when attempting to kdump at the location of a WARN().
853 853
854 = ============================================ 854 = ================================================
855 0 Only WARN(), default behaviour. 855 0 Only WARN(), default behaviour.
856 1 Call panic() after printing out WARN() locat 856 1 Call panic() after printing out WARN() location.
857 = ============================================ 857 = ================================================
858 858
859 859
860 panic_print 860 panic_print
861 =========== 861 ===========
862 862
863 Bitmask for printing system info when panic ha 863 Bitmask for printing system info when panic happens. User can chose
864 combination of the following bits: 864 combination of the following bits:
865 865
866 ===== ======================================= 866 ===== ============================================
867 bit 0 print all tasks info 867 bit 0 print all tasks info
868 bit 1 print system memory info 868 bit 1 print system memory info
869 bit 2 print timer info 869 bit 2 print timer info
870 bit 3 print locks info if ``CONFIG_LOCKDEP`` 870 bit 3 print locks info if ``CONFIG_LOCKDEP`` is on
871 bit 4 print ftrace buffer 871 bit 4 print ftrace buffer
872 bit 5 print all printk messages in buffer 872 bit 5 print all printk messages in buffer
873 bit 6 print all CPUs backtrace (if available 873 bit 6 print all CPUs backtrace (if available in the arch)
874 bit 7 print only tasks in uninterruptible (bl 874 bit 7 print only tasks in uninterruptible (blocked) state
875 ===== ======================================= 875 ===== ============================================
876 876
877 So for example to print tasks and memory info 877 So for example to print tasks and memory info on panic, user can::
878 878
879 echo 3 > /proc/sys/kernel/panic_print 879 echo 3 > /proc/sys/kernel/panic_print
880 880
881 881
882 panic_on_rcu_stall 882 panic_on_rcu_stall
883 ================== 883 ==================
884 884
885 When set to 1, calls panic() after RCU stall d 885 When set to 1, calls panic() after RCU stall detection messages. This
886 is useful to define the root cause of RCU stal 886 is useful to define the root cause of RCU stalls using a vmcore.
887 887
888 = ============================================ 888 = ============================================================
889 0 Do not panic() when RCU stall takes place, d 889 0 Do not panic() when RCU stall takes place, default behavior.
890 1 panic() after printing RCU stall messages. 890 1 panic() after printing RCU stall messages.
891 = ============================================ 891 = ============================================================
892 892
893 max_rcu_stall_to_panic 893 max_rcu_stall_to_panic
894 ====================== 894 ======================
895 895
896 When ``panic_on_rcu_stall`` is set to 1, this 896 When ``panic_on_rcu_stall`` is set to 1, this value determines the
897 number of times that RCU can stall before pani 897 number of times that RCU can stall before panic() is called.
898 898
899 When ``panic_on_rcu_stall`` is set to 0, this 899 When ``panic_on_rcu_stall`` is set to 0, this value is has no effect.
900 900
901 perf_cpu_time_max_percent 901 perf_cpu_time_max_percent
902 ========================= 902 =========================
903 903
904 Hints to the kernel how much CPU time it shoul 904 Hints to the kernel how much CPU time it should be allowed to
905 use to handle perf sampling events. If the pe 905 use to handle perf sampling events. If the perf subsystem
906 is informed that its samples are exceeding thi 906 is informed that its samples are exceeding this limit, it
907 will drop its sampling frequency to attempt to 907 will drop its sampling frequency to attempt to reduce its CPU
908 usage. 908 usage.
909 909
910 Some perf sampling happens in NMIs. If these 910 Some perf sampling happens in NMIs. If these samples
911 unexpectedly take too long to execute, the NMI 911 unexpectedly take too long to execute, the NMIs can become
912 stacked up next to each other so much that not 912 stacked up next to each other so much that nothing else is
913 allowed to execute. 913 allowed to execute.
914 914
915 ===== ======================================== 915 ===== ========================================================
916 0 Disable the mechanism. Do not monitor o 916 0 Disable the mechanism. Do not monitor or correct perf's
917 sampling rate no matter how CPU time it 917 sampling rate no matter how CPU time it takes.
918 918
919 1-100 Attempt to throttle perf's sample rate t 919 1-100 Attempt to throttle perf's sample rate to this
920 percentage of CPU. Note: the kernel cal 920 percentage of CPU. Note: the kernel calculates an
921 "expected" length of each sample event. 921 "expected" length of each sample event. 100 here means
922 100% of that expected length. Even if t 922 100% of that expected length. Even if this is set to
923 100, you may still see sample throttling 923 100, you may still see sample throttling if this
924 length is exceeded. Set to 0 if you tru 924 length is exceeded. Set to 0 if you truly do not care
925 how much CPU is consumed. 925 how much CPU is consumed.
926 ===== ======================================== 926 ===== ========================================================
927 927
928 928
929 perf_event_paranoid 929 perf_event_paranoid
930 =================== 930 ===================
931 931
932 Controls use of the performance events system 932 Controls use of the performance events system by unprivileged
933 users (without CAP_PERFMON). The default valu 933 users (without CAP_PERFMON). The default value is 2.
934 934
935 For backward compatibility reasons access to s 935 For backward compatibility reasons access to system performance
936 monitoring and observability remains open for 936 monitoring and observability remains open for CAP_SYS_ADMIN
937 privileged processes but CAP_SYS_ADMIN usage f 937 privileged processes but CAP_SYS_ADMIN usage for secure system
938 performance monitoring and observability opera 938 performance monitoring and observability operations is discouraged
939 with respect to CAP_PERFMON use cases. 939 with respect to CAP_PERFMON use cases.
940 940
941 === ========================================= 941 === ==================================================================
942 -1 Allow use of (almost) all events by all u 942 -1 Allow use of (almost) all events by all users.
943 943
944 Ignore mlock limit after perf_event_mlock 944 Ignore mlock limit after perf_event_mlock_kb without
945 ``CAP_IPC_LOCK``. 945 ``CAP_IPC_LOCK``.
946 946
947 >=0 Disallow ftrace function tracepoint by us 947 >=0 Disallow ftrace function tracepoint by users without
948 ``CAP_PERFMON``. 948 ``CAP_PERFMON``.
949 949
950 Disallow raw tracepoint access by users w 950 Disallow raw tracepoint access by users without ``CAP_PERFMON``.
951 951
952 >=1 Disallow CPU event access by users withou 952 >=1 Disallow CPU event access by users without ``CAP_PERFMON``.
953 953
954 >=2 Disallow kernel profiling by users withou 954 >=2 Disallow kernel profiling by users without ``CAP_PERFMON``.
955 === ========================================= 955 === ==================================================================
956 956
957 957
958 perf_event_max_stack 958 perf_event_max_stack
959 ==================== 959 ====================
960 960
961 Controls maximum number of stack frames to cop 961 Controls maximum number of stack frames to copy for (``attr.sample_type &
962 PERF_SAMPLE_CALLCHAIN``) configured events, fo 962 PERF_SAMPLE_CALLCHAIN``) configured events, for instance, when using
963 '``perf record -g``' or '``perf trace --call-g 963 '``perf record -g``' or '``perf trace --call-graph fp``'.
964 964
965 This can only be done when no events are in us 965 This can only be done when no events are in use that have callchains
966 enabled, otherwise writing to this file will r 966 enabled, otherwise writing to this file will return ``-EBUSY``.
967 967
968 The default value is 127. 968 The default value is 127.
969 969
970 970
971 perf_event_mlock_kb 971 perf_event_mlock_kb
972 =================== 972 ===================
973 973
974 Control size of per-cpu ring buffer not counte 974 Control size of per-cpu ring buffer not counted against mlock limit.
975 975
976 The default value is 512 + 1 page 976 The default value is 512 + 1 page
977 977
978 978
979 perf_event_max_contexts_per_stack 979 perf_event_max_contexts_per_stack
980 ================================= 980 =================================
981 981
982 Controls maximum number of stack frame context 982 Controls maximum number of stack frame context entries for
983 (``attr.sample_type & PERF_SAMPLE_CALLCHAIN``) 983 (``attr.sample_type & PERF_SAMPLE_CALLCHAIN``) configured events, for
984 instance, when using '``perf record -g``' or ' 984 instance, when using '``perf record -g``' or '``perf trace --call-graph fp``'.
985 985
986 This can only be done when no events are in us 986 This can only be done when no events are in use that have callchains
987 enabled, otherwise writing to this file will r 987 enabled, otherwise writing to this file will return ``-EBUSY``.
988 988
989 The default value is 8. 989 The default value is 8.
990 990
991 991
992 perf_user_access (arm64 and riscv only) 992 perf_user_access (arm64 and riscv only)
993 ======================================= 993 =======================================
994 994
995 Controls user space access for reading perf ev 995 Controls user space access for reading perf event counters.
996 996
997 arm64 997 arm64
998 ===== 998 =====
999 999
1000 The default value is 0 (access disabled). 1000 The default value is 0 (access disabled).
1001 1001
1002 When set to 1, user space can read performanc 1002 When set to 1, user space can read performance monitor counter registers
1003 directly. 1003 directly.
1004 1004
1005 See Documentation/arch/arm64/perf.rst for mor 1005 See Documentation/arch/arm64/perf.rst for more information.
1006 1006
1007 riscv 1007 riscv
1008 ===== 1008 =====
1009 1009
1010 When set to 0, user space access is disabled. 1010 When set to 0, user space access is disabled.
1011 1011
1012 The default value is 1, user space can read p 1012 The default value is 1, user space can read performance monitor counter
1013 registers through perf, any direct access wit 1013 registers through perf, any direct access without perf intervention will trigger
1014 an illegal instruction. 1014 an illegal instruction.
1015 1015
1016 When set to 2, which enables legacy mode (use 1016 When set to 2, which enables legacy mode (user space has direct access to cycle
1017 and insret CSRs only). Note that this legacy 1017 and insret CSRs only). Note that this legacy value is deprecated and will be
1018 removed once all user space applications are 1018 removed once all user space applications are fixed.
1019 1019
1020 Note that the time CSR is always directly acc 1020 Note that the time CSR is always directly accessible to all modes.
1021 1021
1022 pid_max 1022 pid_max
1023 ======= 1023 =======
1024 1024
1025 PID allocation wrap value. When the kernel's 1025 PID allocation wrap value. When the kernel's next PID value
1026 reaches this value, it wraps back to a minimu 1026 reaches this value, it wraps back to a minimum PID value.
1027 PIDs of value ``pid_max`` or larger are not a 1027 PIDs of value ``pid_max`` or larger are not allocated.
1028 1028
1029 1029
1030 ns_last_pid 1030 ns_last_pid
1031 =========== 1031 ===========
1032 1032
1033 The last pid allocated in the current (the on 1033 The last pid allocated in the current (the one task using this sysctl
1034 lives in) pid namespace. When selecting a pid 1034 lives in) pid namespace. When selecting a pid for a next task on fork
1035 kernel tries to allocate a number starting fr 1035 kernel tries to allocate a number starting from this one.
1036 1036
1037 1037
1038 powersave-nap (PPC only) 1038 powersave-nap (PPC only)
1039 ======================== 1039 ========================
1040 1040
1041 If set, Linux-PPC will use the 'nap' mode of 1041 If set, Linux-PPC will use the 'nap' mode of powersaving,
1042 otherwise the 'doze' mode will be used. 1042 otherwise the 'doze' mode will be used.
1043 1043
1044 1044
1045 ============================================= 1045 ==============================================================
1046 1046
1047 printk 1047 printk
1048 ====== 1048 ======
1049 1049
1050 The four values in printk denote: ``console_l 1050 The four values in printk denote: ``console_loglevel``,
1051 ``default_message_loglevel``, ``minimum_conso 1051 ``default_message_loglevel``, ``minimum_console_loglevel`` and
1052 ``default_console_loglevel`` respectively. 1052 ``default_console_loglevel`` respectively.
1053 1053
1054 These values influence printk() behavior when 1054 These values influence printk() behavior when printing or
1055 logging error messages. See '``man 2 syslog`` 1055 logging error messages. See '``man 2 syslog``' for more info on
1056 the different loglevels. 1056 the different loglevels.
1057 1057
1058 ======================== ==================== 1058 ======================== =====================================
1059 console_loglevel messages with a high 1059 console_loglevel messages with a higher priority than
1060 this will be printed 1060 this will be printed to the console
1061 default_message_loglevel messages without an 1061 default_message_loglevel messages without an explicit priority
1062 will be printed with 1062 will be printed with this priority
1063 minimum_console_loglevel minimum (highest) va 1063 minimum_console_loglevel minimum (highest) value to which
1064 console_loglevel can 1064 console_loglevel can be set
1065 default_console_loglevel default value for co 1065 default_console_loglevel default value for console_loglevel
1066 ======================== ==================== 1066 ======================== =====================================
1067 1067
1068 1068
1069 printk_delay 1069 printk_delay
1070 ============ 1070 ============
1071 1071
1072 Delay each printk message in ``printk_delay`` 1072 Delay each printk message in ``printk_delay`` milliseconds
1073 1073
1074 Value from 0 - 10000 is allowed. 1074 Value from 0 - 10000 is allowed.
1075 1075
1076 1076
1077 printk_ratelimit 1077 printk_ratelimit
1078 ================ 1078 ================
1079 1079
1080 Some warning messages are rate limited. ``pri 1080 Some warning messages are rate limited. ``printk_ratelimit`` specifies
1081 the minimum length of time between these mess 1081 the minimum length of time between these messages (in seconds).
1082 The default value is 5 seconds. 1082 The default value is 5 seconds.
1083 1083
1084 A value of 0 will disable rate limiting. 1084 A value of 0 will disable rate limiting.
1085 1085
1086 1086
1087 printk_ratelimit_burst 1087 printk_ratelimit_burst
1088 ====================== 1088 ======================
1089 1089
1090 While long term we enforce one message per `p 1090 While long term we enforce one message per `printk_ratelimit`_
1091 seconds, we do allow a burst of messages to p 1091 seconds, we do allow a burst of messages to pass through.
1092 ``printk_ratelimit_burst`` specifies the numb 1092 ``printk_ratelimit_burst`` specifies the number of messages we can
1093 send before ratelimiting kicks in. 1093 send before ratelimiting kicks in.
1094 1094
1095 The default value is 10 messages. 1095 The default value is 10 messages.
1096 1096
1097 1097
1098 printk_devkmsg 1098 printk_devkmsg
1099 ============== 1099 ==============
1100 1100
1101 Control the logging to ``/dev/kmsg`` from use 1101 Control the logging to ``/dev/kmsg`` from userspace:
1102 1102
1103 ========= =================================== 1103 ========= =============================================
1104 ratelimit default, ratelimited 1104 ratelimit default, ratelimited
1105 on unlimited logging to /dev/kmsg from 1105 on unlimited logging to /dev/kmsg from userspace
1106 off logging to /dev/kmsg disabled 1106 off logging to /dev/kmsg disabled
1107 ========= =================================== 1107 ========= =============================================
1108 1108
1109 The kernel command line parameter ``printk.de 1109 The kernel command line parameter ``printk.devkmsg=`` overrides this and is
1110 a one-time setting until next reboot: once se 1110 a one-time setting until next reboot: once set, it cannot be changed by
1111 this sysctl interface anymore. 1111 this sysctl interface anymore.
1112 1112
1113 ============================================= 1113 ==============================================================
1114 1114
1115 1115
1116 pty 1116 pty
1117 === 1117 ===
1118 1118
1119 See Documentation/filesystems/devpts.rst. 1119 See Documentation/filesystems/devpts.rst.
1120 1120
1121 1121
1122 random 1122 random
1123 ====== 1123 ======
1124 1124
1125 This is a directory, with the following entri 1125 This is a directory, with the following entries:
1126 1126
1127 * ``boot_id``: a UUID generated the first tim 1127 * ``boot_id``: a UUID generated the first time this is retrieved, and
1128 unvarying after that; 1128 unvarying after that;
1129 1129
1130 * ``uuid``: a UUID generated every time this 1130 * ``uuid``: a UUID generated every time this is retrieved (this can
1131 thus be used to generate UUIDs at will); 1131 thus be used to generate UUIDs at will);
1132 1132
1133 * ``entropy_avail``: the pool's entropy count 1133 * ``entropy_avail``: the pool's entropy count, in bits;
1134 1134
1135 * ``poolsize``: the entropy pool size, in bit 1135 * ``poolsize``: the entropy pool size, in bits;
1136 1136
1137 * ``urandom_min_reseed_secs``: obsolete (used 1137 * ``urandom_min_reseed_secs``: obsolete (used to determine the minimum
1138 number of seconds between urandom pool rese 1138 number of seconds between urandom pool reseeding). This file is
1139 writable for compatibility purposes, but wr 1139 writable for compatibility purposes, but writing to it has no effect
1140 on any RNG behavior; 1140 on any RNG behavior;
1141 1141
1142 * ``write_wakeup_threshold``: when the entrop 1142 * ``write_wakeup_threshold``: when the entropy count drops below this
1143 (as a number of bits), processes waiting to 1143 (as a number of bits), processes waiting to write to ``/dev/random``
1144 are woken up. This file is writable for com 1144 are woken up. This file is writable for compatibility purposes, but
1145 writing to it has no effect on any RNG beha 1145 writing to it has no effect on any RNG behavior.
1146 1146
1147 1147
1148 randomize_va_space 1148 randomize_va_space
1149 ================== 1149 ==================
1150 1150
1151 This option can be used to select the type of 1151 This option can be used to select the type of process address
1152 space randomization that is used in the syste 1152 space randomization that is used in the system, for architectures
1153 that support this feature. 1153 that support this feature.
1154 1154
1155 == ========================================= 1155 == ===========================================================================
1156 0 Turn the process address space randomizat 1156 0 Turn the process address space randomization off. This is the
1157 default for architectures that do not sup 1157 default for architectures that do not support this feature anyways,
1158 and kernels that are booted with the "nor 1158 and kernels that are booted with the "norandmaps" parameter.
1159 1159
1160 1 Make the addresses of mmap base, stack an 1160 1 Make the addresses of mmap base, stack and VDSO page randomized.
1161 This, among other things, implies that sh 1161 This, among other things, implies that shared libraries will be
1162 loaded to random addresses. Also for PIE 1162 loaded to random addresses. Also for PIE-linked binaries, the
1163 location of code start is randomized. Th 1163 location of code start is randomized. This is the default if the
1164 ``CONFIG_COMPAT_BRK`` option is enabled. 1164 ``CONFIG_COMPAT_BRK`` option is enabled.
1165 1165
1166 2 Additionally enable heap randomization. 1166 2 Additionally enable heap randomization. This is the default if
1167 ``CONFIG_COMPAT_BRK`` is disabled. 1167 ``CONFIG_COMPAT_BRK`` is disabled.
1168 1168
1169 There are a few legacy applications out t 1169 There are a few legacy applications out there (such as some ancient
1170 versions of libc.so.5 from 1996) that ass 1170 versions of libc.so.5 from 1996) that assume that brk area starts
1171 just after the end of the code+bss. Thes 1171 just after the end of the code+bss. These applications break when
1172 start of the brk area is randomized. The 1172 start of the brk area is randomized. There are however no known
1173 non-legacy applications that would be bro 1173 non-legacy applications that would be broken this way, so for most
1174 systems it is safe to choose full randomi 1174 systems it is safe to choose full randomization.
1175 1175
1176 Systems with ancient and/or broken binari 1176 Systems with ancient and/or broken binaries should be configured
1177 with ``CONFIG_COMPAT_BRK`` enabled, which 1177 with ``CONFIG_COMPAT_BRK`` enabled, which excludes the heap from process
1178 address space randomization. 1178 address space randomization.
1179 == ========================================= 1179 == ===========================================================================
1180 1180
1181 1181
1182 real-root-dev 1182 real-root-dev
1183 ============= 1183 =============
1184 1184
1185 See Documentation/admin-guide/initrd.rst. 1185 See Documentation/admin-guide/initrd.rst.
1186 1186
1187 1187
1188 reboot-cmd (SPARC only) 1188 reboot-cmd (SPARC only)
1189 ======================= 1189 =======================
1190 1190
1191 ??? This seems to be a way to give an argumen 1191 ??? This seems to be a way to give an argument to the Sparc
1192 ROM/Flash boot loader. Maybe to tell it what 1192 ROM/Flash boot loader. Maybe to tell it what to do after
1193 rebooting. ??? 1193 rebooting. ???
1194 1194
1195 1195
1196 sched_energy_aware 1196 sched_energy_aware
1197 ================== 1197 ==================
1198 1198
1199 Enables/disables Energy Aware Scheduling (EAS 1199 Enables/disables Energy Aware Scheduling (EAS). EAS starts
1200 automatically on platforms where it can run ( 1200 automatically on platforms where it can run (that is,
1201 platforms with asymmetric CPU topologies and 1201 platforms with asymmetric CPU topologies and having an Energy
1202 Model available). If your platform happens to 1202 Model available). If your platform happens to meet the
1203 requirements for EAS but you do not want to u 1203 requirements for EAS but you do not want to use it, change
1204 this value to 0. On Non-EAS platforms, write 1204 this value to 0. On Non-EAS platforms, write operation fails and
1205 read doesn't return anything. 1205 read doesn't return anything.
1206 1206
1207 task_delayacct 1207 task_delayacct
1208 =============== 1208 ===============
1209 1209
1210 Enables/disables task delay accounting (see 1210 Enables/disables task delay accounting (see
1211 Documentation/accounting/delay-accounting.rst 1211 Documentation/accounting/delay-accounting.rst. Enabling this feature incurs
1212 a small amount of overhead in the scheduler b 1212 a small amount of overhead in the scheduler but is useful for debugging
1213 and performance tuning. It is required by som 1213 and performance tuning. It is required by some tools such as iotop.
1214 1214
1215 sched_schedstats 1215 sched_schedstats
1216 ================ 1216 ================
1217 1217
1218 Enables/disables scheduler statistics. Enabli 1218 Enables/disables scheduler statistics. Enabling this feature
1219 incurs a small amount of overhead in the sche 1219 incurs a small amount of overhead in the scheduler but is
1220 useful for debugging and performance tuning. 1220 useful for debugging and performance tuning.
1221 1221
1222 sched_util_clamp_min 1222 sched_util_clamp_min
1223 ==================== 1223 ====================
1224 1224
1225 Max allowed *minimum* utilization. 1225 Max allowed *minimum* utilization.
1226 1226
1227 Default value is 1024, which is the maximum p 1227 Default value is 1024, which is the maximum possible value.
1228 1228
1229 It means that any requested uclamp.min value 1229 It means that any requested uclamp.min value cannot be greater than
1230 sched_util_clamp_min, i.e., it is restricted 1230 sched_util_clamp_min, i.e., it is restricted to the range
1231 [0:sched_util_clamp_min]. 1231 [0:sched_util_clamp_min].
1232 1232
1233 sched_util_clamp_max 1233 sched_util_clamp_max
1234 ==================== 1234 ====================
1235 1235
1236 Max allowed *maximum* utilization. 1236 Max allowed *maximum* utilization.
1237 1237
1238 Default value is 1024, which is the maximum p 1238 Default value is 1024, which is the maximum possible value.
1239 1239
1240 It means that any requested uclamp.max value 1240 It means that any requested uclamp.max value cannot be greater than
1241 sched_util_clamp_max, i.e., it is restricted 1241 sched_util_clamp_max, i.e., it is restricted to the range
1242 [0:sched_util_clamp_max]. 1242 [0:sched_util_clamp_max].
1243 1243
1244 sched_util_clamp_min_rt_default 1244 sched_util_clamp_min_rt_default
1245 =============================== 1245 ===============================
1246 1246
1247 By default Linux is tuned for performance. Wh 1247 By default Linux is tuned for performance. Which means that RT tasks always run
1248 at the highest frequency and most capable (hi 1248 at the highest frequency and most capable (highest capacity) CPU (in
1249 heterogeneous systems). 1249 heterogeneous systems).
1250 1250
1251 Uclamp achieves this by setting the requested 1251 Uclamp achieves this by setting the requested uclamp.min of all RT tasks to
1252 1024 by default, which effectively boosts the 1252 1024 by default, which effectively boosts the tasks to run at the highest
1253 frequency and biases them to run on the bigge 1253 frequency and biases them to run on the biggest CPU.
1254 1254
1255 This knob allows admins to change the default 1255 This knob allows admins to change the default behavior when uclamp is being
1256 used. In battery powered devices particularly 1256 used. In battery powered devices particularly, running at the maximum
1257 capacity and frequency will increase energy c 1257 capacity and frequency will increase energy consumption and shorten the battery
1258 life. 1258 life.
1259 1259
1260 This knob is only effective for RT tasks whic 1260 This knob is only effective for RT tasks which the user hasn't modified their
1261 requested uclamp.min value via sched_setattr( 1261 requested uclamp.min value via sched_setattr() syscall.
1262 1262
1263 This knob will not escape the range constrain 1263 This knob will not escape the range constraint imposed by sched_util_clamp_min
1264 defined above. 1264 defined above.
1265 1265
1266 For example if 1266 For example if
1267 1267
1268 sched_util_clamp_min_rt_default = 800 1268 sched_util_clamp_min_rt_default = 800
1269 sched_util_clamp_min = 600 1269 sched_util_clamp_min = 600
1270 1270
1271 Then the boost will be clamped to 600 because 1271 Then the boost will be clamped to 600 because 800 is outside of the permissible
1272 range of [0:600]. This could happen for insta 1272 range of [0:600]. This could happen for instance if a powersave mode will
1273 restrict all boosts temporarily by modifying 1273 restrict all boosts temporarily by modifying sched_util_clamp_min. As soon as
1274 this restriction is lifted, the requested sch 1274 this restriction is lifted, the requested sched_util_clamp_min_rt_default
1275 will take effect. 1275 will take effect.
1276 1276
1277 seccomp 1277 seccomp
1278 ======= 1278 =======
1279 1279
1280 See Documentation/userspace-api/seccomp_filte 1280 See Documentation/userspace-api/seccomp_filter.rst.
1281 1281
1282 1282
1283 sg-big-buff 1283 sg-big-buff
1284 =========== 1284 ===========
1285 1285
1286 This file shows the size of the generic SCSI 1286 This file shows the size of the generic SCSI (sg) buffer.
1287 You can't tune it just yet, but you could cha 1287 You can't tune it just yet, but you could change it on
1288 compile time by editing ``include/scsi/sg.h`` 1288 compile time by editing ``include/scsi/sg.h`` and changing
1289 the value of ``SG_BIG_BUFF``. 1289 the value of ``SG_BIG_BUFF``.
1290 1290
1291 There shouldn't be any reason to change this 1291 There shouldn't be any reason to change this value. If
1292 you can come up with one, you probably know w 1292 you can come up with one, you probably know what you
1293 are doing anyway :) 1293 are doing anyway :)
1294 1294
1295 1295
1296 shmall 1296 shmall
1297 ====== 1297 ======
1298 1298
1299 This parameter sets the total amount of share 1299 This parameter sets the total amount of shared memory pages that can be used
1300 inside ipc namespace. The shared memory pages 1300 inside ipc namespace. The shared memory pages counting occurs for each ipc
1301 namespace separately and is not inherited. He 1301 namespace separately and is not inherited. Hence, ``shmall`` should always be at
1302 least ``ceil(shmmax/PAGE_SIZE)``. 1302 least ``ceil(shmmax/PAGE_SIZE)``.
1303 1303
1304 If you are not sure what the default ``PAGE_S 1304 If you are not sure what the default ``PAGE_SIZE`` is on your Linux
1305 system, you can run the following command:: 1305 system, you can run the following command::
1306 1306
1307 # getconf PAGE_SIZE 1307 # getconf PAGE_SIZE
1308 1308
1309 To reduce or disable the ability to allocate 1309 To reduce or disable the ability to allocate shared memory, you must create a
1310 new ipc namespace, set this parameter to the 1310 new ipc namespace, set this parameter to the required value and prohibit the
1311 creation of a new ipc namespace in the curren 1311 creation of a new ipc namespace in the current user namespace or cgroups can
1312 be used. 1312 be used.
1313 1313
1314 shmmax 1314 shmmax
1315 ====== 1315 ======
1316 1316
1317 This value can be used to query and set the r 1317 This value can be used to query and set the run time limit
1318 on the maximum shared memory segment size tha 1318 on the maximum shared memory segment size that can be created.
1319 Shared memory segments up to 1Gb are now supp 1319 Shared memory segments up to 1Gb are now supported in the
1320 kernel. This value defaults to ``SHMMAX``. 1320 kernel. This value defaults to ``SHMMAX``.
1321 1321
1322 1322
1323 shmmni 1323 shmmni
1324 ====== 1324 ======
1325 1325
1326 This value determines the maximum number of s 1326 This value determines the maximum number of shared memory segments.
1327 4096 by default (``SHMMNI``). 1327 4096 by default (``SHMMNI``).
1328 1328
1329 1329
1330 shm_rmid_forced 1330 shm_rmid_forced
1331 =============== 1331 ===============
1332 1332
1333 Linux lets you set resource limits, including 1333 Linux lets you set resource limits, including how much memory one
1334 process can consume, via ``setrlimit(2)``. U 1334 process can consume, via ``setrlimit(2)``. Unfortunately, shared memory
1335 segments are allowed to exist without associa 1335 segments are allowed to exist without association with any process, and
1336 thus might not be counted against any resourc 1336 thus might not be counted against any resource limits. If enabled,
1337 shared memory segments are automatically dest 1337 shared memory segments are automatically destroyed when their attach
1338 count becomes zero after a detach or a proces 1338 count becomes zero after a detach or a process termination. It will
1339 also destroy segments that were created, but 1339 also destroy segments that were created, but never attached to, on exit
1340 from the process. The only use left for ``IP 1340 from the process. The only use left for ``IPC_RMID`` is to immediately
1341 destroy an unattached segment. Of course, th 1341 destroy an unattached segment. Of course, this breaks the way things are
1342 defined, so some applications might stop work 1342 defined, so some applications might stop working. Note that this
1343 feature will do you no good unless you also c 1343 feature will do you no good unless you also configure your resource
1344 limits (in particular, ``RLIMIT_AS`` and ``RL 1344 limits (in particular, ``RLIMIT_AS`` and ``RLIMIT_NPROC``). Most systems don't
1345 need this. 1345 need this.
1346 1346
1347 Note that if you change this from 0 to 1, alr 1347 Note that if you change this from 0 to 1, already created segments
1348 without users and with a dead originative pro 1348 without users and with a dead originative process will be destroyed.
1349 1349
1350 1350
1351 sysctl_writes_strict 1351 sysctl_writes_strict
1352 ==================== 1352 ====================
1353 1353
1354 Control how file position affects the behavio 1354 Control how file position affects the behavior of updating sysctl values
1355 via the ``/proc/sys`` interface: 1355 via the ``/proc/sys`` interface:
1356 1356
1357 == ====================================== 1357 == ======================================================================
1358 -1 Legacy per-write sysctl value handling 1358 -1 Legacy per-write sysctl value handling, with no printk warnings.
1359 Each write syscall must fully contain 1359 Each write syscall must fully contain the sysctl value to be
1360 written, and multiple writes on the sa 1360 written, and multiple writes on the same sysctl file descriptor
1361 will rewrite the sysctl value, regardl 1361 will rewrite the sysctl value, regardless of file position.
1362 0 Same behavior as above, but warn about 1362 0 Same behavior as above, but warn about processes that perform writes
1363 to a sysctl file descriptor when the f 1363 to a sysctl file descriptor when the file position is not 0.
1364 1 (default) Respect file position when w 1364 1 (default) Respect file position when writing sysctl strings. Multiple
1365 writes will append to the sysctl value 1365 writes will append to the sysctl value buffer. Anything past the max
1366 length of the sysctl value buffer will 1366 length of the sysctl value buffer will be ignored. Writes to numeric
1367 sysctl entries must always be at file 1367 sysctl entries must always be at file position 0 and the value must
1368 be fully contained in the buffer sent 1368 be fully contained in the buffer sent in the write syscall.
1369 == ====================================== 1369 == ======================================================================
1370 1370
1371 1371
1372 softlockup_all_cpu_backtrace 1372 softlockup_all_cpu_backtrace
1373 ============================ 1373 ============================
1374 1374
1375 This value controls the soft lockup detector 1375 This value controls the soft lockup detector thread's behavior
1376 when a soft lockup condition is detected as t 1376 when a soft lockup condition is detected as to whether or not
1377 to gather further debug information. If enabl 1377 to gather further debug information. If enabled, each cpu will
1378 be issued an NMI and instructed to capture st 1378 be issued an NMI and instructed to capture stack trace.
1379 1379
1380 This feature is only applicable for architect 1380 This feature is only applicable for architectures which support
1381 NMI. 1381 NMI.
1382 1382
1383 = =========================================== 1383 = ============================================
1384 0 Do nothing. This is the default behavior. 1384 0 Do nothing. This is the default behavior.
1385 1 On detection capture more debug information 1385 1 On detection capture more debug information.
1386 = =========================================== 1386 = ============================================
1387 1387
1388 1388
1389 softlockup_panic 1389 softlockup_panic
1390 ================= 1390 =================
1391 1391
1392 This parameter can be used to control whether 1392 This parameter can be used to control whether the kernel panics
1393 when a soft lockup is detected. 1393 when a soft lockup is detected.
1394 1394
1395 = =========================================== 1395 = ============================================
1396 0 Don't panic on soft lockup. 1396 0 Don't panic on soft lockup.
1397 1 Panic on soft lockup. 1397 1 Panic on soft lockup.
1398 = =========================================== 1398 = ============================================
1399 1399
1400 This can also be set using the softlockup_pan 1400 This can also be set using the softlockup_panic kernel parameter.
1401 1401
1402 1402
1403 soft_watchdog 1403 soft_watchdog
1404 ============= 1404 =============
1405 1405
1406 This parameter can be used to control the sof 1406 This parameter can be used to control the soft lockup detector.
1407 1407
1408 = ================================= 1408 = =================================
1409 0 Disable the soft lockup detector. 1409 0 Disable the soft lockup detector.
1410 1 Enable the soft lockup detector. 1410 1 Enable the soft lockup detector.
1411 = ================================= 1411 = =================================
1412 1412
1413 The soft lockup detector monitors CPUs for th 1413 The soft lockup detector monitors CPUs for threads that are hogging the CPUs
1414 without rescheduling voluntarily, and thus pr 1414 without rescheduling voluntarily, and thus prevent the 'migration/N' threads
1415 from running, causing the watchdog work fail 1415 from running, causing the watchdog work fail to execute. The mechanism depends
1416 on the CPUs ability to respond to timer inter 1416 on the CPUs ability to respond to timer interrupts which are needed for the
1417 watchdog work to be queued by the watchdog ti 1417 watchdog work to be queued by the watchdog timer function, otherwise the NMI
1418 watchdog — if enabled — can detect a hard 1418 watchdog — if enabled — can detect a hard lockup condition.
1419 1419
1420 1420
1421 split_lock_mitigate (x86 only) 1421 split_lock_mitigate (x86 only)
1422 ============================== 1422 ==============================
1423 1423
1424 On x86, each "split lock" imposes a system-wi 1424 On x86, each "split lock" imposes a system-wide performance penalty. On larger
1425 systems, large numbers of split locks from un 1425 systems, large numbers of split locks from unprivileged users can result in
1426 denials of service to well-behaved and potent 1426 denials of service to well-behaved and potentially more important users.
1427 1427
1428 The kernel mitigates these bad users by detec 1428 The kernel mitigates these bad users by detecting split locks and imposing
1429 penalties: forcing them to wait and only allo 1429 penalties: forcing them to wait and only allowing one core to execute split
1430 locks at a time. 1430 locks at a time.
1431 1431
1432 These mitigations can make those bad applicat 1432 These mitigations can make those bad applications unbearably slow. Setting
1433 split_lock_mitigate=0 may restore some applic 1433 split_lock_mitigate=0 may restore some application performance, but will also
1434 increase system exposure to denial of service 1434 increase system exposure to denial of service attacks from split lock users.
1435 1435
1436 = =========================================== 1436 = ===================================================================
1437 0 Disable the mitigation mode - just warns th 1437 0 Disable the mitigation mode - just warns the split lock on kernel log
1438 and exposes the system to denials of servic 1438 and exposes the system to denials of service from the split lockers.
1439 1 Enable the mitigation mode (this is the def 1439 1 Enable the mitigation mode (this is the default) - penalizes the split
1440 lockers with intentional performance degrad 1440 lockers with intentional performance degradation.
1441 = =========================================== 1441 = ===================================================================
1442 1442
1443 1443
1444 stack_erasing 1444 stack_erasing
1445 ============= 1445 =============
1446 1446
1447 This parameter can be used to control kernel 1447 This parameter can be used to control kernel stack erasing at the end
1448 of syscalls for kernels built with ``CONFIG_G 1448 of syscalls for kernels built with ``CONFIG_GCC_PLUGIN_STACKLEAK``.
1449 1449
1450 That erasing reduces the information which ke 1450 That erasing reduces the information which kernel stack leak bugs
1451 can reveal and blocks some uninitialized stac 1451 can reveal and blocks some uninitialized stack variable attacks.
1452 The tradeoff is the performance impact: on a 1452 The tradeoff is the performance impact: on a single CPU system kernel
1453 compilation sees a 1% slowdown, other systems 1453 compilation sees a 1% slowdown, other systems and workloads may vary.
1454 1454
1455 = =========================================== 1455 = ====================================================================
1456 0 Kernel stack erasing is disabled, STACKLEAK 1456 0 Kernel stack erasing is disabled, STACKLEAK_METRICS are not updated.
1457 1 Kernel stack erasing is enabled (default), 1457 1 Kernel stack erasing is enabled (default), it is performed before
1458 returning to the userspace at the end of sy 1458 returning to the userspace at the end of syscalls.
1459 = =========================================== 1459 = ====================================================================
1460 1460
1461 1461
1462 stop-a (SPARC only) 1462 stop-a (SPARC only)
1463 =================== 1463 ===================
1464 1464
1465 Controls Stop-A: 1465 Controls Stop-A:
1466 1466
1467 = ==================================== 1467 = ====================================
1468 0 Stop-A has no effect. 1468 0 Stop-A has no effect.
1469 1 Stop-A breaks to the PROM (default). 1469 1 Stop-A breaks to the PROM (default).
1470 = ==================================== 1470 = ====================================
1471 1471
1472 Stop-A is always enabled on a panic, so that 1472 Stop-A is always enabled on a panic, so that the user can return to
1473 the boot PROM. 1473 the boot PROM.
1474 1474
1475 1475
1476 sysrq 1476 sysrq
1477 ===== 1477 =====
1478 1478
1479 See Documentation/admin-guide/sysrq.rst. 1479 See Documentation/admin-guide/sysrq.rst.
1480 1480
1481 1481
1482 tainted 1482 tainted
1483 ======= 1483 =======
1484 1484
1485 Non-zero if the kernel has been tainted. Nume 1485 Non-zero if the kernel has been tainted. Numeric values, which can be
1486 ORed together. The letters are seen in "Taint 1486 ORed together. The letters are seen in "Tainted" line of Oops reports.
1487 1487
1488 ====== ===== ============================== 1488 ====== ===== ==============================================================
1489 1 `(P)` proprietary module was loaded 1489 1 `(P)` proprietary module was loaded
1490 2 `(F)` module was force loaded 1490 2 `(F)` module was force loaded
1491 4 `(S)` kernel running on an out of sp 1491 4 `(S)` kernel running on an out of specification system
1492 8 `(R)` module was force unloaded 1492 8 `(R)` module was force unloaded
1493 16 `(M)` processor reported a Machine C 1493 16 `(M)` processor reported a Machine Check Exception (MCE)
1494 32 `(B)` bad page referenced or some un 1494 32 `(B)` bad page referenced or some unexpected page flags
1495 64 `(U)` taint requested by userspace a 1495 64 `(U)` taint requested by userspace application
1496 128 `(D)` kernel died recently, i.e. the 1496 128 `(D)` kernel died recently, i.e. there was an OOPS or BUG
1497 256 `(A)` an ACPI table was overridden b 1497 256 `(A)` an ACPI table was overridden by user
1498 512 `(W)` kernel issued warning 1498 512 `(W)` kernel issued warning
1499 1024 `(C)` staging driver was loaded 1499 1024 `(C)` staging driver was loaded
1500 2048 `(I)` workaround for bug in platform 1500 2048 `(I)` workaround for bug in platform firmware applied
1501 4096 `(O)` externally-built ("out-of-tree 1501 4096 `(O)` externally-built ("out-of-tree") module was loaded
1502 8192 `(E)` unsigned module was loaded 1502 8192 `(E)` unsigned module was loaded
1503 16384 `(L)` soft lockup occurred 1503 16384 `(L)` soft lockup occurred
1504 32768 `(K)` kernel has been live patched 1504 32768 `(K)` kernel has been live patched
1505 65536 `(X)` Auxiliary taint, defined and u 1505 65536 `(X)` Auxiliary taint, defined and used by for distros
1506 131072 `(T)` The kernel was built with the 1506 131072 `(T)` The kernel was built with the struct randomization plugin
1507 ====== ===== ============================== 1507 ====== ===== ==============================================================
1508 1508
1509 See Documentation/admin-guide/tainted-kernels 1509 See Documentation/admin-guide/tainted-kernels.rst for more information.
1510 1510
1511 Note: 1511 Note:
1512 writes to this sysctl interface will fail w 1512 writes to this sysctl interface will fail with ``EINVAL`` if the kernel is
1513 booted with the command line option ``panic 1513 booted with the command line option ``panic_on_taint=<bitmask>,nousertaint``
1514 and any of the ORed together values being w 1514 and any of the ORed together values being written to ``tainted`` match with
1515 the bitmask declared on panic_on_taint. 1515 the bitmask declared on panic_on_taint.
1516 See Documentation/admin-guide/kernel-parame 1516 See Documentation/admin-guide/kernel-parameters.rst for more details on
1517 that particular kernel command line option 1517 that particular kernel command line option and its optional
1518 ``nousertaint`` switch. 1518 ``nousertaint`` switch.
1519 1519
1520 threads-max 1520 threads-max
1521 =========== 1521 ===========
1522 1522
1523 This value controls the maximum number of thr 1523 This value controls the maximum number of threads that can be created
1524 using ``fork()``. 1524 using ``fork()``.
1525 1525
1526 During initialization the kernel sets this va 1526 During initialization the kernel sets this value such that even if the
1527 maximum number of threads is created, the thr 1527 maximum number of threads is created, the thread structures occupy only
1528 a part (1/8th) of the available RAM pages. 1528 a part (1/8th) of the available RAM pages.
1529 1529
1530 The minimum value that can be written to ``th 1530 The minimum value that can be written to ``threads-max`` is 1.
1531 1531
1532 The maximum value that can be written to ``th 1532 The maximum value that can be written to ``threads-max`` is given by the
1533 constant ``FUTEX_TID_MASK`` (0x3fffffff). 1533 constant ``FUTEX_TID_MASK`` (0x3fffffff).
1534 1534
1535 If a value outside of this range is written t 1535 If a value outside of this range is written to ``threads-max`` an
1536 ``EINVAL`` error occurs. 1536 ``EINVAL`` error occurs.
1537 1537
1538 1538
1539 traceoff_on_warning 1539 traceoff_on_warning
1540 =================== 1540 ===================
1541 1541
1542 When set, disables tracing (see Documentation 1542 When set, disables tracing (see Documentation/trace/ftrace.rst) when a
1543 ``WARN()`` is hit. 1543 ``WARN()`` is hit.
1544 1544
1545 1545
1546 tracepoint_printk 1546 tracepoint_printk
1547 ================= 1547 =================
1548 1548
1549 When tracepoints are sent to printk() (enable 1549 When tracepoints are sent to printk() (enabled by the ``tp_printk``
1550 boot parameter), this entry provides runtime 1550 boot parameter), this entry provides runtime control::
1551 1551
1552 echo 0 > /proc/sys/kernel/tracepoint_prin 1552 echo 0 > /proc/sys/kernel/tracepoint_printk
1553 1553
1554 will stop tracepoints from being sent to prin 1554 will stop tracepoints from being sent to printk(), and::
1555 1555
1556 echo 1 > /proc/sys/kernel/tracepoint_prin 1556 echo 1 > /proc/sys/kernel/tracepoint_printk
1557 1557
1558 will send them to printk() again. 1558 will send them to printk() again.
1559 1559
1560 This only works if the kernel was booted with 1560 This only works if the kernel was booted with ``tp_printk`` enabled.
1561 1561
1562 See Documentation/admin-guide/kernel-paramete 1562 See Documentation/admin-guide/kernel-parameters.rst and
1563 Documentation/trace/boottime-trace.rst. 1563 Documentation/trace/boottime-trace.rst.
1564 1564
1565 1565
1566 unaligned-trap 1566 unaligned-trap
1567 ============== 1567 ==============
1568 1568
1569 On architectures where unaligned accesses cau 1569 On architectures where unaligned accesses cause traps, and where this
1570 feature is supported (``CONFIG_SYSCTL_ARCH_UN 1570 feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_ALLOW``; currently,
1571 ``arc``, ``parisc`` and ``loongarch``), contr 1571 ``arc``, ``parisc`` and ``loongarch``), controls whether unaligned traps
1572 are caught and emulated (instead of failing). 1572 are caught and emulated (instead of failing).
1573 1573
1574 = =========================================== 1574 = ========================================================
1575 0 Do not emulate unaligned accesses. 1575 0 Do not emulate unaligned accesses.
1576 1 Emulate unaligned accesses. This is the def 1576 1 Emulate unaligned accesses. This is the default setting.
1577 = =========================================== 1577 = ========================================================
1578 1578
1579 See also `ignore-unaligned-usertrap`_. 1579 See also `ignore-unaligned-usertrap`_.
1580 1580
1581 1581
1582 unknown_nmi_panic 1582 unknown_nmi_panic
1583 ================= 1583 =================
1584 1584
1585 The value in this file affects behavior of ha 1585 The value in this file affects behavior of handling NMI. When the
1586 value is non-zero, unknown NMI is trapped and 1586 value is non-zero, unknown NMI is trapped and then panic occurs. At
1587 that time, kernel debugging information is di 1587 that time, kernel debugging information is displayed on console.
1588 1588
1589 NMI switch that most IA32 servers have fires 1589 NMI switch that most IA32 servers have fires unknown NMI up, for
1590 example. If a system hangs up, try pressing 1590 example. If a system hangs up, try pressing the NMI switch.
1591 1591
1592 1592
1593 unprivileged_bpf_disabled 1593 unprivileged_bpf_disabled
1594 ========================= 1594 =========================
1595 1595
1596 Writing 1 to this entry will disable unprivil 1596 Writing 1 to this entry will disable unprivileged calls to ``bpf()``;
1597 once disabled, calling ``bpf()`` without ``CA 1597 once disabled, calling ``bpf()`` without ``CAP_SYS_ADMIN`` or ``CAP_BPF``
1598 will return ``-EPERM``. Once set to 1, this c 1598 will return ``-EPERM``. Once set to 1, this can't be cleared from the
1599 running kernel anymore. 1599 running kernel anymore.
1600 1600
1601 Writing 2 to this entry will also disable unp 1601 Writing 2 to this entry will also disable unprivileged calls to ``bpf()``,
1602 however, an admin can still change this setti 1602 however, an admin can still change this setting later on, if needed, by
1603 writing 0 or 1 to this entry. 1603 writing 0 or 1 to this entry.
1604 1604
1605 If ``BPF_UNPRIV_DEFAULT_OFF`` is enabled in t 1605 If ``BPF_UNPRIV_DEFAULT_OFF`` is enabled in the kernel config, then this
1606 entry will default to 2 instead of 0. 1606 entry will default to 2 instead of 0.
1607 1607
1608 = =========================================== 1608 = =============================================================
1609 0 Unprivileged calls to ``bpf()`` are enabled 1609 0 Unprivileged calls to ``bpf()`` are enabled
1610 1 Unprivileged calls to ``bpf()`` are disable 1610 1 Unprivileged calls to ``bpf()`` are disabled without recovery
1611 2 Unprivileged calls to ``bpf()`` are disable 1611 2 Unprivileged calls to ``bpf()`` are disabled
1612 = =========================================== 1612 = =============================================================
1613 1613
1614 1614
1615 warn_limit 1615 warn_limit
1616 ========== 1616 ==========
1617 1617
1618 Number of kernel warnings after which the ker 1618 Number of kernel warnings after which the kernel should panic when
1619 ``panic_on_warn`` is not set. Setting this to 1619 ``panic_on_warn`` is not set. Setting this to 0 disables checking
1620 the warning count. Setting this to 1 has the 1620 the warning count. Setting this to 1 has the same effect as setting
1621 ``panic_on_warn=1``. The default value is 0. 1621 ``panic_on_warn=1``. The default value is 0.
1622 1622
1623 1623
1624 watchdog 1624 watchdog
1625 ======== 1625 ========
1626 1626
1627 This parameter can be used to disable or enab 1627 This parameter can be used to disable or enable the soft lockup detector
1628 *and* the NMI watchdog (i.e. the hard lockup 1628 *and* the NMI watchdog (i.e. the hard lockup detector) at the same time.
1629 1629
1630 = ============================== 1630 = ==============================
1631 0 Disable both lockup detectors. 1631 0 Disable both lockup detectors.
1632 1 Enable both lockup detectors. 1632 1 Enable both lockup detectors.
1633 = ============================== 1633 = ==============================
1634 1634
1635 The soft lockup detector and the NMI watchdog 1635 The soft lockup detector and the NMI watchdog can also be disabled or
1636 enabled individually, using the ``soft_watchd 1636 enabled individually, using the ``soft_watchdog`` and ``nmi_watchdog``
1637 parameters. 1637 parameters.
1638 If the ``watchdog`` parameter is read, for ex 1638 If the ``watchdog`` parameter is read, for example by executing::
1639 1639
1640 cat /proc/sys/kernel/watchdog 1640 cat /proc/sys/kernel/watchdog
1641 1641
1642 the output of this command (0 or 1) shows the 1642 the output of this command (0 or 1) shows the logical OR of
1643 ``soft_watchdog`` and ``nmi_watchdog``. 1643 ``soft_watchdog`` and ``nmi_watchdog``.
1644 1644
1645 1645
1646 watchdog_cpumask 1646 watchdog_cpumask
1647 ================ 1647 ================
1648 1648
1649 This value can be used to control on which cp 1649 This value can be used to control on which cpus the watchdog may run.
1650 The default cpumask is all possible cores, bu 1650 The default cpumask is all possible cores, but if ``NO_HZ_FULL`` is
1651 enabled in the kernel config, and cores are s 1651 enabled in the kernel config, and cores are specified with the
1652 ``nohz_full=`` boot argument, those cores are 1652 ``nohz_full=`` boot argument, those cores are excluded by default.
1653 Offline cores can be included in this mask, a 1653 Offline cores can be included in this mask, and if the core is later
1654 brought online, the watchdog will be started 1654 brought online, the watchdog will be started based on the mask value.
1655 1655
1656 Typically this value would only be touched in 1656 Typically this value would only be touched in the ``nohz_full`` case
1657 to re-enable cores that by default were not r 1657 to re-enable cores that by default were not running the watchdog,
1658 if a kernel lockup was suspected on those cor 1658 if a kernel lockup was suspected on those cores.
1659 1659
1660 The argument value is the standard cpulist fo 1660 The argument value is the standard cpulist format for cpumasks,
1661 so for example to enable the watchdog on core 1661 so for example to enable the watchdog on cores 0, 2, 3, and 4 you
1662 might say:: 1662 might say::
1663 1663
1664 echo 0,2-4 > /proc/sys/kernel/watchdog_cpum 1664 echo 0,2-4 > /proc/sys/kernel/watchdog_cpumask
1665 1665
1666 1666
1667 watchdog_thresh 1667 watchdog_thresh
1668 =============== 1668 ===============
1669 1669
1670 This value can be used to control the frequen 1670 This value can be used to control the frequency of hrtimer and NMI
1671 events and the soft and hard lockup threshold 1671 events and the soft and hard lockup thresholds. The default threshold
1672 is 10 seconds. 1672 is 10 seconds.
1673 1673
1674 The softlockup threshold is (``2 * watchdog_t 1674 The softlockup threshold is (``2 * watchdog_thresh``). Setting this
1675 tunable to zero will disable lockup detection 1675 tunable to zero will disable lockup detection altogether.
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