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 Dump the buffer of the CPU that triggered the oops.
303 oops. !! 303 = ===================================================
304 <instance> Dump the specific inst <<
305 <instance>=2(orig_cpu) Dump the specific inst <<
306 that triggered the oop <<
307 ======================= ====================== <<
308 <<
309 Multiple instance dump is also supported, and <<
310 by commas. If global buffer also needs to be d <<
311 the dump mode (1/2/orig_cpu) first for global <<
312 <<
313 So for example to dump "foo" and "bar" instanc <<
314 user can:: <<
315 <<
316 echo "foo,bar" > /proc/sys/kernel/ftrace_dum <<
317 <<
318 To dump global buffer and "foo" instance buffe <<
319 CPUs along with the "bar" instance buffer on C <<
320 oops, user can:: <<
321 304
322 echo "1,foo,bar=2" > /proc/sys/kernel/ftrace <<
323 305
324 ftrace_enabled, stack_tracer_enabled 306 ftrace_enabled, stack_tracer_enabled
325 ==================================== 307 ====================================
326 308
327 See Documentation/trace/ftrace.rst. 309 See Documentation/trace/ftrace.rst.
328 310
329 311
330 hardlockup_all_cpu_backtrace 312 hardlockup_all_cpu_backtrace
331 ============================ 313 ============================
332 314
333 This value controls the hard lockup detector b 315 This value controls the hard lockup detector behavior when a hard
334 lockup condition is detected as to whether or 316 lockup condition is detected as to whether or not to gather further
335 debug information. If enabled, arch-specific a 317 debug information. If enabled, arch-specific all-CPU stack dumping
336 will be initiated. 318 will be initiated.
337 319
338 = ============================================ 320 = ============================================
339 0 Do nothing. This is the default behavior. 321 0 Do nothing. This is the default behavior.
340 1 On detection capture more debug information. 322 1 On detection capture more debug information.
341 = ============================================ 323 = ============================================
342 324
343 325
344 hardlockup_panic 326 hardlockup_panic
345 ================ 327 ================
346 328
347 This parameter can be used to control whether 329 This parameter can be used to control whether the kernel panics
348 when a hard lockup is detected. 330 when a hard lockup is detected.
349 331
350 = =========================== 332 = ===========================
351 0 Don't panic on hard lockup. 333 0 Don't panic on hard lockup.
352 1 Panic on hard lockup. 334 1 Panic on hard lockup.
353 = =========================== 335 = ===========================
354 336
355 See Documentation/admin-guide/lockup-watchdogs 337 See Documentation/admin-guide/lockup-watchdogs.rst for more information.
356 This can also be set using the nmi_watchdog ke 338 This can also be set using the nmi_watchdog kernel parameter.
357 339
358 340
359 hotplug 341 hotplug
360 ======= 342 =======
361 343
362 Path for the hotplug policy agent. 344 Path for the hotplug policy agent.
363 Default value is ``CONFIG_UEVENT_HELPER_PATH`` 345 Default value is ``CONFIG_UEVENT_HELPER_PATH``, which in turn defaults
364 to the empty string. 346 to the empty string.
365 347
366 This file only exists when ``CONFIG_UEVENT_HEL 348 This file only exists when ``CONFIG_UEVENT_HELPER`` is enabled. Most
367 modern systems rely exclusively on the netlink 349 modern systems rely exclusively on the netlink-based uevent source and
368 don't need this. 350 don't need this.
369 351
370 352
371 hung_task_all_cpu_backtrace 353 hung_task_all_cpu_backtrace
372 =========================== 354 ===========================
373 355
374 If this option is set, the kernel will send an 356 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. 357 their backtraces when a hung task is detected. This file shows up if
376 CONFIG_DETECT_HUNG_TASK and CONFIG_SMP are ena 358 CONFIG_DETECT_HUNG_TASK and CONFIG_SMP are enabled.
377 359
378 0: Won't show all CPUs backtraces when a hung 360 0: Won't show all CPUs backtraces when a hung task is detected.
379 This is the default behavior. 361 This is the default behavior.
380 362
381 1: Will non-maskably interrupt all CPUs and du 363 1: Will non-maskably interrupt all CPUs and dump their backtraces when
382 a hung task is detected. 364 a hung task is detected.
383 365
384 366
385 hung_task_panic 367 hung_task_panic
386 =============== 368 ===============
387 369
388 Controls the kernel's behavior when a hung tas 370 Controls the kernel's behavior when a hung task is detected.
389 This file shows up if ``CONFIG_DETECT_HUNG_TAS 371 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
390 372
391 = ============================================ 373 = =================================================
392 0 Continue operation. This is the default beha 374 0 Continue operation. This is the default behavior.
393 1 Panic immediately. 375 1 Panic immediately.
394 = ============================================ 376 = =================================================
395 377
396 378
397 hung_task_check_count 379 hung_task_check_count
398 ===================== 380 =====================
399 381
400 The upper bound on the number of tasks that ar 382 The upper bound on the number of tasks that are checked.
401 This file shows up if ``CONFIG_DETECT_HUNG_TAS 383 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
402 384
403 385
404 hung_task_timeout_secs 386 hung_task_timeout_secs
405 ====================== 387 ======================
406 388
407 When a task in D state did not get scheduled 389 When a task in D state did not get scheduled
408 for more than this value report a warning. 390 for more than this value report a warning.
409 This file shows up if ``CONFIG_DETECT_HUNG_TAS 391 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
410 392
411 0 means infinite timeout, no checking is done. 393 0 means infinite timeout, no checking is done.
412 394
413 Possible values to set are in range {0:``LONG_ 395 Possible values to set are in range {0:``LONG_MAX``/``HZ``}.
414 396
415 397
416 hung_task_check_interval_secs 398 hung_task_check_interval_secs
417 ============================= 399 =============================
418 400
419 Hung task check interval. If hung task checkin 401 Hung task check interval. If hung task checking is enabled
420 (see `hung_task_timeout_secs`_), the check is 402 (see `hung_task_timeout_secs`_), the check is done every
421 ``hung_task_check_interval_secs`` seconds. 403 ``hung_task_check_interval_secs`` seconds.
422 This file shows up if ``CONFIG_DETECT_HUNG_TAS 404 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
423 405
424 0 (default) means use ``hung_task_timeout_secs 406 0 (default) means use ``hung_task_timeout_secs`` as checking
425 interval. 407 interval.
426 408
427 Possible values to set are in range {0:``LONG_ 409 Possible values to set are in range {0:``LONG_MAX``/``HZ``}.
428 410
429 411
430 hung_task_warnings 412 hung_task_warnings
431 ================== 413 ==================
432 414
433 The maximum number of warnings to report. Duri 415 The maximum number of warnings to report. During a check interval
434 if a hung task is detected, this value is decr 416 if a hung task is detected, this value is decreased by 1.
435 When this value reaches 0, no more warnings wi 417 When this value reaches 0, no more warnings will be reported.
436 This file shows up if ``CONFIG_DETECT_HUNG_TAS 418 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
437 419
438 -1: report an infinite number of warnings. 420 -1: report an infinite number of warnings.
439 421
440 422
441 hyperv_record_panic_msg 423 hyperv_record_panic_msg
442 ======================= 424 =======================
443 425
444 Controls whether the panic kmsg data should be 426 Controls whether the panic kmsg data should be reported to Hyper-V.
445 427
446 = ============================================ 428 = =========================================================
447 0 Do not report panic kmsg data. 429 0 Do not report panic kmsg data.
448 1 Report the panic kmsg data. This is the defa 430 1 Report the panic kmsg data. This is the default behavior.
449 = ============================================ 431 = =========================================================
450 432
451 433
452 ignore-unaligned-usertrap 434 ignore-unaligned-usertrap
453 ========================= 435 =========================
454 436
455 On architectures where unaligned accesses caus 437 On architectures where unaligned accesses cause traps, and where this
456 feature is supported (``CONFIG_SYSCTL_ARCH_UNA 438 feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_NO_WARN``;
457 currently, ``arc``, ``parisc`` and ``loongarch !! 439 currently, ``arc``, ``ia64`` and ``loongarch``), controls whether all
458 unaligned traps are logged. 440 unaligned traps are logged.
459 441
460 = ============================================ 442 = =============================================================
461 0 Log all unaligned accesses. 443 0 Log all unaligned accesses.
462 1 Only warn the first time a process traps. Th 444 1 Only warn the first time a process traps. This is the default
463 setting. 445 setting.
464 = ============================================ 446 = =============================================================
465 447
466 See also `unaligned-trap`_. !! 448 See also `unaligned-trap`_ and `unaligned-dump-stack`_. On ``ia64``,
>> 449 this allows system administrators to override the
>> 450 ``IA64_THREAD_UAC_NOPRINT`` ``prctl`` and avoid logs being flooded.
>> 451
467 452
468 io_uring_disabled 453 io_uring_disabled
469 ================= 454 =================
470 455
471 Prevents all processes from creating new io_ur 456 Prevents all processes from creating new io_uring instances. Enabling this
472 shrinks the kernel's attack surface. 457 shrinks the kernel's attack surface.
473 458
474 = ============================================ 459 = ======================================================================
475 0 All processes can create io_uring instances 460 0 All processes can create io_uring instances as normal. This is the
476 default setting. 461 default setting.
477 1 io_uring creation is disabled (io_uring_setu 462 1 io_uring creation is disabled (io_uring_setup() will fail with
478 -EPERM) for unprivileged processes not in th 463 -EPERM) for unprivileged processes not in the io_uring_group group.
479 Existing io_uring instances can still be use 464 Existing io_uring instances can still be used. See the
480 documentation for io_uring_group for more in 465 documentation for io_uring_group for more information.
481 2 io_uring creation is disabled for all proces 466 2 io_uring creation is disabled for all processes. io_uring_setup()
482 always fails with -EPERM. Existing io_uring 467 always fails with -EPERM. Existing io_uring instances can still be
483 used. 468 used.
484 = ============================================ 469 = ======================================================================
485 470
486 471
487 io_uring_group 472 io_uring_group
488 ============== 473 ==============
489 474
490 When io_uring_disabled is set to 1, a process 475 When io_uring_disabled is set to 1, a process must either be
491 privileged (CAP_SYS_ADMIN) or be in the io_uri 476 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 477 to create an io_uring instance. If io_uring_group is set to -1 (the
493 default), only processes with the CAP_SYS_ADMI 478 default), only processes with the CAP_SYS_ADMIN capability may create
494 io_uring instances. 479 io_uring instances.
495 480
496 481
497 kexec_load_disabled 482 kexec_load_disabled
498 =================== 483 ===================
499 484
500 A toggle indicating if the syscalls ``kexec_lo 485 A toggle indicating if the syscalls ``kexec_load`` and
501 ``kexec_file_load`` have been disabled. 486 ``kexec_file_load`` have been disabled.
502 This value defaults to 0 (false: ``kexec_*load 487 This value defaults to 0 (false: ``kexec_*load`` enabled), but can be
503 set to 1 (true: ``kexec_*load`` disabled). 488 set to 1 (true: ``kexec_*load`` disabled).
504 Once true, kexec can no longer be used, and th 489 Once true, kexec can no longer be used, and the toggle cannot be set
505 back to false. 490 back to false.
506 This allows a kexec image to be loaded before 491 This allows a kexec image to be loaded before disabling the syscall,
507 allowing a system to set up (and later use) an 492 allowing a system to set up (and later use) an image without it being
508 altered. 493 altered.
509 Generally used together with the `modules_disa 494 Generally used together with the `modules_disabled`_ sysctl.
510 495
511 kexec_load_limit_panic 496 kexec_load_limit_panic
512 ====================== 497 ======================
513 498
514 This parameter specifies a limit to the number 499 This parameter specifies a limit to the number of times the syscalls
515 ``kexec_load`` and ``kexec_file_load`` can be 500 ``kexec_load`` and ``kexec_file_load`` can be called with a crash
516 image. It can only be set with a more restrict 501 image. It can only be set with a more restrictive value than the
517 current one. 502 current one.
518 503
519 == =========================================== 504 == ======================================================
520 -1 Unlimited calls to kexec. This is the defau 505 -1 Unlimited calls to kexec. This is the default setting.
521 N Number of calls left. 506 N Number of calls left.
522 == =========================================== 507 == ======================================================
523 508
524 kexec_load_limit_reboot 509 kexec_load_limit_reboot
525 ======================= 510 =======================
526 511
527 Similar functionality as ``kexec_load_limit_pa 512 Similar functionality as ``kexec_load_limit_panic``, but for a normal
528 image. 513 image.
529 514
530 kptr_restrict 515 kptr_restrict
531 ============= 516 =============
532 517
533 This toggle indicates whether restrictions are 518 This toggle indicates whether restrictions are placed on
534 exposing kernel addresses via ``/proc`` and ot 519 exposing kernel addresses via ``/proc`` and other interfaces.
535 520
536 When ``kptr_restrict`` is set to 0 (the defaul 521 When ``kptr_restrict`` is set to 0 (the default) the address is hashed
537 before printing. 522 before printing.
538 (This is the equivalent to %p.) 523 (This is the equivalent to %p.)
539 524
540 When ``kptr_restrict`` is set to 1, kernel poi 525 When ``kptr_restrict`` is set to 1, kernel pointers printed using the
541 %pK format specifier will be replaced with 0s 526 %pK format specifier will be replaced with 0s unless the user has
542 ``CAP_SYSLOG`` and effective user and group id 527 ``CAP_SYSLOG`` and effective user and group ids are equal to the real
543 ids. 528 ids.
544 This is because %pK checks are done at read() 529 This is because %pK checks are done at read() time rather than open()
545 time, so if permissions are elevated between t 530 time, so if permissions are elevated between the open() and the read()
546 (e.g via a setuid binary) then %pK will not le 531 (e.g via a setuid binary) then %pK will not leak kernel pointers to
547 unprivileged users. 532 unprivileged users.
548 Note, this is a temporary solution only. 533 Note, this is a temporary solution only.
549 The correct long-term solution is to do the pe 534 The correct long-term solution is to do the permission checks at
550 open() time. 535 open() time.
551 Consider removing world read permissions from 536 Consider removing world read permissions from files that use %pK, and
552 using `dmesg_restrict`_ to protect against use 537 using `dmesg_restrict`_ to protect against uses of %pK in ``dmesg(8)``
553 if leaking kernel pointer values to unprivileg 538 if leaking kernel pointer values to unprivileged users is a concern.
554 539
555 When ``kptr_restrict`` is set to 2, kernel poi 540 When ``kptr_restrict`` is set to 2, kernel pointers printed using
556 %pK will be replaced with 0s regardless of pri 541 %pK will be replaced with 0s regardless of privileges.
557 542
558 543
559 modprobe 544 modprobe
560 ======== 545 ========
561 546
562 The full path to the usermode helper for autol 547 The full path to the usermode helper for autoloading kernel modules,
563 by default ``CONFIG_MODPROBE_PATH``, which in 548 by default ``CONFIG_MODPROBE_PATH``, which in turn defaults to
564 "/sbin/modprobe". This binary is executed whe 549 "/sbin/modprobe". This binary is executed when the kernel requests a
565 module. For example, if userspace passes an u 550 module. For example, if userspace passes an unknown filesystem type
566 to mount(), then the kernel will automatically 551 to mount(), then the kernel will automatically request the
567 corresponding filesystem module by executing t 552 corresponding filesystem module by executing this usermode helper.
568 This usermode helper should insert the needed 553 This usermode helper should insert the needed module into the kernel.
569 554
570 This sysctl only affects module autoloading. 555 This sysctl only affects module autoloading. It has no effect on the
571 ability to explicitly insert modules. 556 ability to explicitly insert modules.
572 557
573 This sysctl can be used to debug module loadin 558 This sysctl can be used to debug module loading requests::
574 559
575 echo '#! /bin/sh' > /tmp/modprobe 560 echo '#! /bin/sh' > /tmp/modprobe
576 echo 'echo "$@" >> /tmp/modprobe.log' >> / 561 echo 'echo "$@" >> /tmp/modprobe.log' >> /tmp/modprobe
577 echo 'exec /sbin/modprobe "$@"' >> /tmp/mo 562 echo 'exec /sbin/modprobe "$@"' >> /tmp/modprobe
578 chmod a+x /tmp/modprobe 563 chmod a+x /tmp/modprobe
579 echo /tmp/modprobe > /proc/sys/kernel/modp 564 echo /tmp/modprobe > /proc/sys/kernel/modprobe
580 565
581 Alternatively, if this sysctl is set to the em 566 Alternatively, if this sysctl is set to the empty string, then module
582 autoloading is completely disabled. The kerne 567 autoloading is completely disabled. The kernel will not try to
583 execute a usermode helper at all, nor will it 568 execute a usermode helper at all, nor will it call the
584 kernel_module_request LSM hook. 569 kernel_module_request LSM hook.
585 570
586 If CONFIG_STATIC_USERMODEHELPER=y is set in th 571 If CONFIG_STATIC_USERMODEHELPER=y is set in the kernel configuration,
587 then the configured static usermode helper ove 572 then the configured static usermode helper overrides this sysctl,
588 except that the empty string is still accepted 573 except that the empty string is still accepted to completely disable
589 module autoloading as described above. 574 module autoloading as described above.
590 575
591 modules_disabled 576 modules_disabled
592 ================ 577 ================
593 578
594 A toggle value indicating if modules are allow 579 A toggle value indicating if modules are allowed to be loaded
595 in an otherwise modular kernel. This toggle d 580 in an otherwise modular kernel. This toggle defaults to off
596 (0), but can be set true (1). Once true, modu 581 (0), but can be set true (1). Once true, modules can be
597 neither loaded nor unloaded, and the toggle ca 582 neither loaded nor unloaded, and the toggle cannot be set back
598 to false. Generally used with the `kexec_load 583 to false. Generally used with the `kexec_load_disabled`_ toggle.
599 584
600 585
601 .. _msgmni: 586 .. _msgmni:
602 587
603 msgmax, msgmnb, and msgmni 588 msgmax, msgmnb, and msgmni
604 ========================== 589 ==========================
605 590
606 ``msgmax`` is the maximum size of an IPC messa 591 ``msgmax`` is the maximum size of an IPC message, in bytes. 8192 by
607 default (``MSGMAX``). 592 default (``MSGMAX``).
608 593
609 ``msgmnb`` is the maximum size of an IPC queue 594 ``msgmnb`` is the maximum size of an IPC queue, in bytes. 16384 by
610 default (``MSGMNB``). 595 default (``MSGMNB``).
611 596
612 ``msgmni`` is the maximum number of IPC queues 597 ``msgmni`` is the maximum number of IPC queues. 32000 by default
613 (``MSGMNI``). 598 (``MSGMNI``).
614 599
615 All of these parameters are set per ipc namesp <<
616 in POSIX message queues is limited by ``RLIMIT <<
617 respected hierarchically in the each user name <<
618 600
619 msg_next_id, sem_next_id, and shm_next_id (Sys 601 msg_next_id, sem_next_id, and shm_next_id (System V IPC)
620 ============================================== 602 ========================================================
621 603
622 These three toggles allows to specify desired 604 These three toggles allows to specify desired id for next allocated IPC
623 object: message, semaphore or shared memory re 605 object: message, semaphore or shared memory respectively.
624 606
625 By default they are equal to -1, which means g 607 By default they are equal to -1, which means generic allocation logic.
626 Possible values to set are in range {0:``INT_M 608 Possible values to set are in range {0:``INT_MAX``}.
627 609
628 Notes: 610 Notes:
629 1) kernel doesn't guarantee, that new object 611 1) kernel doesn't guarantee, that new object will have desired id. So,
630 it's up to userspace, how to handle an ob 612 it's up to userspace, how to handle an object with "wrong" id.
631 2) Toggle with non-default value will be set 613 2) Toggle with non-default value will be set back to -1 by kernel after
632 successful IPC object allocation. If an I 614 successful IPC object allocation. If an IPC object allocation syscall
633 fails, it is undefined if the value remai 615 fails, it is undefined if the value remains unmodified or is reset to -1.
634 616
635 617
636 ngroups_max 618 ngroups_max
637 =========== 619 ===========
638 620
639 Maximum number of supplementary groups, _i.e._ 621 Maximum number of supplementary groups, _i.e._ the maximum size which
640 ``setgroups`` will accept. Exports ``NGROUPS_M 622 ``setgroups`` will accept. Exports ``NGROUPS_MAX`` from the kernel.
641 623
642 624
643 625
644 nmi_watchdog 626 nmi_watchdog
645 ============ 627 ============
646 628
647 This parameter can be used to control the NMI 629 This parameter can be used to control the NMI watchdog
648 (i.e. the hard lockup detector) on x86 systems 630 (i.e. the hard lockup detector) on x86 systems.
649 631
650 = ================================= 632 = =================================
651 0 Disable the hard lockup detector. 633 0 Disable the hard lockup detector.
652 1 Enable the hard lockup detector. 634 1 Enable the hard lockup detector.
653 = ================================= 635 = =================================
654 636
655 The hard lockup detector monitors each CPU for 637 The hard lockup detector monitors each CPU for its ability to respond to
656 timer interrupts. The mechanism utilizes CPU p 638 timer interrupts. The mechanism utilizes CPU performance counter registers
657 that are programmed to generate Non-Maskable I 639 that are programmed to generate Non-Maskable Interrupts (NMIs) periodically
658 while a CPU is busy. Hence, the alternative na 640 while a CPU is busy. Hence, the alternative name 'NMI watchdog'.
659 641
660 The NMI watchdog is disabled by default if the 642 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 643 in a KVM virtual machine. This default can be overridden by adding::
662 644
663 nmi_watchdog=1 645 nmi_watchdog=1
664 646
665 to the guest kernel command line (see 647 to the guest kernel command line (see
666 Documentation/admin-guide/kernel-parameters.rs 648 Documentation/admin-guide/kernel-parameters.rst).
667 649
668 650
669 nmi_wd_lpm_factor (PPC only) 651 nmi_wd_lpm_factor (PPC only)
670 ============================ 652 ============================
671 653
672 Factor to apply to the NMI watchdog timeout (o 654 Factor to apply to the NMI watchdog timeout (only when ``nmi_watchdog`` is
673 set to 1). This factor represents the percenta 655 set to 1). This factor represents the percentage added to
674 ``watchdog_thresh`` when calculating the NMI w 656 ``watchdog_thresh`` when calculating the NMI watchdog timeout during an
675 LPM. The soft lockup timeout is not impacted. 657 LPM. The soft lockup timeout is not impacted.
676 658
677 A value of 0 means no change. The default valu 659 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 660 watchdog is set to 30s (based on ``watchdog_thresh`` equal to 10).
679 661
680 662
681 numa_balancing 663 numa_balancing
682 ============== 664 ==============
683 665
684 Enables/disables and configures automatic page 666 Enables/disables and configures automatic page fault based NUMA memory
685 balancing. Memory is moved automatically to n 667 balancing. Memory is moved automatically to nodes that access it often.
686 The value to set can be the result of ORing th 668 The value to set can be the result of ORing the following:
687 669
688 = ================================= 670 = =================================
689 0 NUMA_BALANCING_DISABLED 671 0 NUMA_BALANCING_DISABLED
690 1 NUMA_BALANCING_NORMAL 672 1 NUMA_BALANCING_NORMAL
691 2 NUMA_BALANCING_MEMORY_TIERING 673 2 NUMA_BALANCING_MEMORY_TIERING
692 = ================================= 674 = =================================
693 675
694 Or NUMA_BALANCING_NORMAL to optimize page plac 676 Or NUMA_BALANCING_NORMAL to optimize page placement among different
695 NUMA nodes to reduce remote accessing. On NUM 677 NUMA nodes to reduce remote accessing. On NUMA machines, there is a
696 performance penalty if remote memory is access 678 performance penalty if remote memory is accessed by a CPU. When this
697 feature is enabled the kernel samples what tas 679 feature is enabled the kernel samples what task thread is accessing
698 memory by periodically unmapping pages and lat 680 memory by periodically unmapping pages and later trapping a page
699 fault. At the time of the page fault, it is de 681 fault. At the time of the page fault, it is determined if the data
700 being accessed should be migrated to a local m 682 being accessed should be migrated to a local memory node.
701 683
702 The unmapping of pages and trapping faults inc 684 The unmapping of pages and trapping faults incur additional overhead that
703 ideally is offset by improved memory locality 685 ideally is offset by improved memory locality but there is no universal
704 guarantee. If the target workload is already b 686 guarantee. If the target workload is already bound to NUMA nodes then this
705 feature should be disabled. 687 feature should be disabled.
706 688
707 Or NUMA_BALANCING_MEMORY_TIERING to optimize p 689 Or NUMA_BALANCING_MEMORY_TIERING to optimize page placement among
708 different types of memory (represented as diff 690 different types of memory (represented as different NUMA nodes) to
709 place the hot pages in the fast memory. This 691 place the hot pages in the fast memory. This is implemented based on
710 unmapping and page fault too. 692 unmapping and page fault too.
711 693
712 numa_balancing_promote_rate_limit_MBps 694 numa_balancing_promote_rate_limit_MBps
713 ====================================== 695 ======================================
714 696
715 Too high promotion/demotion throughput between 697 Too high promotion/demotion throughput between different memory types
716 may hurt application latency. This can be use 698 may hurt application latency. This can be used to rate limit the
717 promotion throughput. The per-node max promot 699 promotion throughput. The per-node max promotion throughput in MB/s
718 will be limited to be no more than the set val 700 will be limited to be no more than the set value.
719 701
720 A rule of thumb is to set this to less than 1/ 702 A rule of thumb is to set this to less than 1/10 of the PMEM node
721 write bandwidth. 703 write bandwidth.
722 704
723 oops_all_cpu_backtrace 705 oops_all_cpu_backtrace
724 ====================== 706 ======================
725 707
726 If this option is set, the kernel will send an 708 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 709 their backtraces when an oops event occurs. It should be used as a last
728 resort in case a panic cannot be triggered (to 710 resort in case a panic cannot be triggered (to protect VMs running, for
729 example) or kdump can't be collected. This fil 711 example) or kdump can't be collected. This file shows up if CONFIG_SMP
730 is enabled. 712 is enabled.
731 713
732 0: Won't show all CPUs backtraces when an oops 714 0: Won't show all CPUs backtraces when an oops is detected.
733 This is the default behavior. 715 This is the default behavior.
734 716
735 1: Will non-maskably interrupt all CPUs and du 717 1: Will non-maskably interrupt all CPUs and dump their backtraces when
736 an oops event is detected. 718 an oops event is detected.
737 719
738 720
739 oops_limit 721 oops_limit
740 ========== 722 ==========
741 723
742 Number of kernel oopses after which the kernel 724 Number of kernel oopses after which the kernel should panic when
743 ``panic_on_oops`` is not set. Setting this to 725 ``panic_on_oops`` is not set. Setting this to 0 disables checking
744 the count. Setting this to 1 has the same eff 726 the count. Setting this to 1 has the same effect as setting
745 ``panic_on_oops=1``. The default value is 1000 727 ``panic_on_oops=1``. The default value is 10000.
746 728
747 729
748 osrelease, ostype & version 730 osrelease, ostype & version
749 =========================== 731 ===========================
750 732
751 :: 733 ::
752 734
753 # cat osrelease 735 # cat osrelease
754 2.1.88 736 2.1.88
755 # cat ostype 737 # cat ostype
756 Linux 738 Linux
757 # cat version 739 # cat version
758 #5 Wed Feb 25 21:49:24 MET 1998 740 #5 Wed Feb 25 21:49:24 MET 1998
759 741
760 The files ``osrelease`` and ``ostype`` should 742 The files ``osrelease`` and ``ostype`` should be clear enough.
761 ``version`` 743 ``version``
762 needs a little more clarification however. The 744 needs a little more clarification however. The '#5' means that
763 this is the fifth kernel built from this sourc 745 this is the fifth kernel built from this source base and the
764 date behind it indicates the time the kernel w 746 date behind it indicates the time the kernel was built.
765 The only way to tune these values is to rebuil 747 The only way to tune these values is to rebuild the kernel :-)
766 748
767 749
768 overflowgid & overflowuid 750 overflowgid & overflowuid
769 ========================= 751 =========================
770 752
771 if your architecture did not always support 32 753 if your architecture did not always support 32-bit UIDs (i.e. arm,
772 i386, m68k, sh, and sparc32), a fixed UID and 754 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 755 applications that use the old 16-bit UID/GID system calls, if the
774 actual UID or GID would exceed 65535. 756 actual UID or GID would exceed 65535.
775 757
776 These sysctls allow you to change the value of 758 These sysctls allow you to change the value of the fixed UID and GID.
777 The default is 65534. 759 The default is 65534.
778 760
779 761
780 panic 762 panic
781 ===== 763 =====
782 764
783 The value in this file determines the behaviou 765 The value in this file determines the behaviour of the kernel on a
784 panic: 766 panic:
785 767
786 * if zero, the kernel will loop forever; 768 * if zero, the kernel will loop forever;
787 * if negative, the kernel will reboot immediat 769 * if negative, the kernel will reboot immediately;
788 * if positive, the kernel will reboot after th 770 * if positive, the kernel will reboot after the corresponding number
789 of seconds. 771 of seconds.
790 772
791 When you use the software watchdog, the recomm 773 When you use the software watchdog, the recommended setting is 60.
792 774
793 775
794 panic_on_io_nmi 776 panic_on_io_nmi
795 =============== 777 ===============
796 778
797 Controls the kernel's behavior when a CPU rece 779 Controls the kernel's behavior when a CPU receives an NMI caused by
798 an IO error. 780 an IO error.
799 781
800 = ============================================ 782 = ==================================================================
801 0 Try to continue operation (default). 783 0 Try to continue operation (default).
802 1 Panic immediately. The IO error triggered an 784 1 Panic immediately. The IO error triggered an NMI. This indicates a
803 serious system condition which could result 785 serious system condition which could result in IO data corruption.
804 Rather than continuing, panicking might be a 786 Rather than continuing, panicking might be a better choice. Some
805 servers issue this sort of NMI when the dump 787 servers issue this sort of NMI when the dump button is pushed,
806 and you can use this option to take a crash 788 and you can use this option to take a crash dump.
807 = ============================================ 789 = ==================================================================
808 790
809 791
810 panic_on_oops 792 panic_on_oops
811 ============= 793 =============
812 794
813 Controls the kernel's behaviour when an oops o 795 Controls the kernel's behaviour when an oops or BUG is encountered.
814 796
815 = ============================================ 797 = ===================================================================
816 0 Try to continue operation. 798 0 Try to continue operation.
817 1 Panic immediately. If the `panic` sysctl is 799 1 Panic immediately. If the `panic` sysctl is also non-zero then the
818 machine will be rebooted. 800 machine will be rebooted.
819 = ============================================ 801 = ===================================================================
820 802
821 803
822 panic_on_stackoverflow 804 panic_on_stackoverflow
823 ====================== 805 ======================
824 806
825 Controls the kernel's behavior when detecting 807 Controls the kernel's behavior when detecting the overflows of
826 kernel, IRQ and exception stacks except a user 808 kernel, IRQ and exception stacks except a user stack.
827 This file shows up if ``CONFIG_DEBUG_STACKOVER 809 This file shows up if ``CONFIG_DEBUG_STACKOVERFLOW`` is enabled.
828 810
829 = ========================== 811 = ==========================
830 0 Try to continue operation. 812 0 Try to continue operation.
831 1 Panic immediately. 813 1 Panic immediately.
832 = ========================== 814 = ==========================
833 815
834 816
835 panic_on_unrecovered_nmi 817 panic_on_unrecovered_nmi
836 ======================== 818 ========================
837 819
838 The default Linux behaviour on an NMI of eithe 820 The default Linux behaviour on an NMI of either memory or unknown is
839 to continue operation. For many environments s 821 to continue operation. For many environments such as scientific
840 computing it is preferable that the box is tak 822 computing it is preferable that the box is taken out and the error
841 dealt with than an uncorrected parity/ECC erro 823 dealt with than an uncorrected parity/ECC error get propagated.
842 824
843 A small number of systems do generate NMIs for 825 A small number of systems do generate NMIs for bizarre random reasons
844 such as power management so the default is off 826 such as power management so the default is off. That sysctl works like
845 the existing panic controls already in that di 827 the existing panic controls already in that directory.
846 828
847 829
848 panic_on_warn 830 panic_on_warn
849 ============= 831 =============
850 832
851 Calls panic() in the WARN() path when set to 1 833 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 834 a kernel rebuild when attempting to kdump at the location of a WARN().
853 835
854 = ============================================ 836 = ================================================
855 0 Only WARN(), default behaviour. 837 0 Only WARN(), default behaviour.
856 1 Call panic() after printing out WARN() locat 838 1 Call panic() after printing out WARN() location.
857 = ============================================ 839 = ================================================
858 840
859 841
860 panic_print 842 panic_print
861 =========== 843 ===========
862 844
863 Bitmask for printing system info when panic ha 845 Bitmask for printing system info when panic happens. User can chose
864 combination of the following bits: 846 combination of the following bits:
865 847
866 ===== ======================================= 848 ===== ============================================
867 bit 0 print all tasks info 849 bit 0 print all tasks info
868 bit 1 print system memory info 850 bit 1 print system memory info
869 bit 2 print timer info 851 bit 2 print timer info
870 bit 3 print locks info if ``CONFIG_LOCKDEP`` 852 bit 3 print locks info if ``CONFIG_LOCKDEP`` is on
871 bit 4 print ftrace buffer 853 bit 4 print ftrace buffer
872 bit 5 print all printk messages in buffer 854 bit 5 print all printk messages in buffer
873 bit 6 print all CPUs backtrace (if available 855 bit 6 print all CPUs backtrace (if available in the arch)
874 bit 7 print only tasks in uninterruptible (bl <<
875 ===== ======================================= 856 ===== ============================================
876 857
877 So for example to print tasks and memory info 858 So for example to print tasks and memory info on panic, user can::
878 859
879 echo 3 > /proc/sys/kernel/panic_print 860 echo 3 > /proc/sys/kernel/panic_print
880 861
881 862
882 panic_on_rcu_stall 863 panic_on_rcu_stall
883 ================== 864 ==================
884 865
885 When set to 1, calls panic() after RCU stall d 866 When set to 1, calls panic() after RCU stall detection messages. This
886 is useful to define the root cause of RCU stal 867 is useful to define the root cause of RCU stalls using a vmcore.
887 868
888 = ============================================ 869 = ============================================================
889 0 Do not panic() when RCU stall takes place, d 870 0 Do not panic() when RCU stall takes place, default behavior.
890 1 panic() after printing RCU stall messages. 871 1 panic() after printing RCU stall messages.
891 = ============================================ 872 = ============================================================
892 873
893 max_rcu_stall_to_panic 874 max_rcu_stall_to_panic
894 ====================== 875 ======================
895 876
896 When ``panic_on_rcu_stall`` is set to 1, this 877 When ``panic_on_rcu_stall`` is set to 1, this value determines the
897 number of times that RCU can stall before pani 878 number of times that RCU can stall before panic() is called.
898 879
899 When ``panic_on_rcu_stall`` is set to 0, this 880 When ``panic_on_rcu_stall`` is set to 0, this value is has no effect.
900 881
901 perf_cpu_time_max_percent 882 perf_cpu_time_max_percent
902 ========================= 883 =========================
903 884
904 Hints to the kernel how much CPU time it shoul 885 Hints to the kernel how much CPU time it should be allowed to
905 use to handle perf sampling events. If the pe 886 use to handle perf sampling events. If the perf subsystem
906 is informed that its samples are exceeding thi 887 is informed that its samples are exceeding this limit, it
907 will drop its sampling frequency to attempt to 888 will drop its sampling frequency to attempt to reduce its CPU
908 usage. 889 usage.
909 890
910 Some perf sampling happens in NMIs. If these 891 Some perf sampling happens in NMIs. If these samples
911 unexpectedly take too long to execute, the NMI 892 unexpectedly take too long to execute, the NMIs can become
912 stacked up next to each other so much that not 893 stacked up next to each other so much that nothing else is
913 allowed to execute. 894 allowed to execute.
914 895
915 ===== ======================================== 896 ===== ========================================================
916 0 Disable the mechanism. Do not monitor o 897 0 Disable the mechanism. Do not monitor or correct perf's
917 sampling rate no matter how CPU time it 898 sampling rate no matter how CPU time it takes.
918 899
919 1-100 Attempt to throttle perf's sample rate t 900 1-100 Attempt to throttle perf's sample rate to this
920 percentage of CPU. Note: the kernel cal 901 percentage of CPU. Note: the kernel calculates an
921 "expected" length of each sample event. 902 "expected" length of each sample event. 100 here means
922 100% of that expected length. Even if t 903 100% of that expected length. Even if this is set to
923 100, you may still see sample throttling 904 100, you may still see sample throttling if this
924 length is exceeded. Set to 0 if you tru 905 length is exceeded. Set to 0 if you truly do not care
925 how much CPU is consumed. 906 how much CPU is consumed.
926 ===== ======================================== 907 ===== ========================================================
927 908
928 909
929 perf_event_paranoid 910 perf_event_paranoid
930 =================== 911 ===================
931 912
932 Controls use of the performance events system 913 Controls use of the performance events system by unprivileged
933 users (without CAP_PERFMON). The default valu 914 users (without CAP_PERFMON). The default value is 2.
934 915
935 For backward compatibility reasons access to s 916 For backward compatibility reasons access to system performance
936 monitoring and observability remains open for 917 monitoring and observability remains open for CAP_SYS_ADMIN
937 privileged processes but CAP_SYS_ADMIN usage f 918 privileged processes but CAP_SYS_ADMIN usage for secure system
938 performance monitoring and observability opera 919 performance monitoring and observability operations is discouraged
939 with respect to CAP_PERFMON use cases. 920 with respect to CAP_PERFMON use cases.
940 921
941 === ========================================= 922 === ==================================================================
942 -1 Allow use of (almost) all events by all u 923 -1 Allow use of (almost) all events by all users.
943 924
944 Ignore mlock limit after perf_event_mlock 925 Ignore mlock limit after perf_event_mlock_kb without
945 ``CAP_IPC_LOCK``. 926 ``CAP_IPC_LOCK``.
946 927
947 >=0 Disallow ftrace function tracepoint by us 928 >=0 Disallow ftrace function tracepoint by users without
948 ``CAP_PERFMON``. 929 ``CAP_PERFMON``.
949 930
950 Disallow raw tracepoint access by users w 931 Disallow raw tracepoint access by users without ``CAP_PERFMON``.
951 932
952 >=1 Disallow CPU event access by users withou 933 >=1 Disallow CPU event access by users without ``CAP_PERFMON``.
953 934
954 >=2 Disallow kernel profiling by users withou 935 >=2 Disallow kernel profiling by users without ``CAP_PERFMON``.
955 === ========================================= 936 === ==================================================================
956 937
957 938
958 perf_event_max_stack 939 perf_event_max_stack
959 ==================== 940 ====================
960 941
961 Controls maximum number of stack frames to cop 942 Controls maximum number of stack frames to copy for (``attr.sample_type &
962 PERF_SAMPLE_CALLCHAIN``) configured events, fo 943 PERF_SAMPLE_CALLCHAIN``) configured events, for instance, when using
963 '``perf record -g``' or '``perf trace --call-g 944 '``perf record -g``' or '``perf trace --call-graph fp``'.
964 945
965 This can only be done when no events are in us 946 This can only be done when no events are in use that have callchains
966 enabled, otherwise writing to this file will r 947 enabled, otherwise writing to this file will return ``-EBUSY``.
967 948
968 The default value is 127. 949 The default value is 127.
969 950
970 951
971 perf_event_mlock_kb 952 perf_event_mlock_kb
972 =================== 953 ===================
973 954
974 Control size of per-cpu ring buffer not counte 955 Control size of per-cpu ring buffer not counted against mlock limit.
975 956
976 The default value is 512 + 1 page 957 The default value is 512 + 1 page
977 958
978 959
979 perf_event_max_contexts_per_stack 960 perf_event_max_contexts_per_stack
980 ================================= 961 =================================
981 962
982 Controls maximum number of stack frame context 963 Controls maximum number of stack frame context entries for
983 (``attr.sample_type & PERF_SAMPLE_CALLCHAIN``) 964 (``attr.sample_type & PERF_SAMPLE_CALLCHAIN``) configured events, for
984 instance, when using '``perf record -g``' or ' 965 instance, when using '``perf record -g``' or '``perf trace --call-graph fp``'.
985 966
986 This can only be done when no events are in us 967 This can only be done when no events are in use that have callchains
987 enabled, otherwise writing to this file will r 968 enabled, otherwise writing to this file will return ``-EBUSY``.
988 969
989 The default value is 8. 970 The default value is 8.
990 971
991 972
992 perf_user_access (arm64 and riscv only) 973 perf_user_access (arm64 and riscv only)
993 ======================================= 974 =======================================
994 975
995 Controls user space access for reading perf ev 976 Controls user space access for reading perf event counters.
996 977
997 arm64 978 arm64
998 ===== 979 =====
999 980
1000 The default value is 0 (access disabled). 981 The default value is 0 (access disabled).
1001 982
1002 When set to 1, user space can read performanc 983 When set to 1, user space can read performance monitor counter registers
1003 directly. 984 directly.
1004 985
1005 See Documentation/arch/arm64/perf.rst for mor 986 See Documentation/arch/arm64/perf.rst for more information.
1006 987
1007 riscv 988 riscv
1008 ===== 989 =====
1009 990
1010 When set to 0, user space access is disabled. 991 When set to 0, user space access is disabled.
1011 992
1012 The default value is 1, user space can read p 993 The default value is 1, user space can read performance monitor counter
1013 registers through perf, any direct access wit 994 registers through perf, any direct access without perf intervention will trigger
1014 an illegal instruction. 995 an illegal instruction.
1015 996
1016 When set to 2, which enables legacy mode (use 997 When set to 2, which enables legacy mode (user space has direct access to cycle
1017 and insret CSRs only). Note that this legacy 998 and insret CSRs only). Note that this legacy value is deprecated and will be
1018 removed once all user space applications are 999 removed once all user space applications are fixed.
1019 1000
1020 Note that the time CSR is always directly acc 1001 Note that the time CSR is always directly accessible to all modes.
1021 1002
1022 pid_max 1003 pid_max
1023 ======= 1004 =======
1024 1005
1025 PID allocation wrap value. When the kernel's 1006 PID allocation wrap value. When the kernel's next PID value
1026 reaches this value, it wraps back to a minimu 1007 reaches this value, it wraps back to a minimum PID value.
1027 PIDs of value ``pid_max`` or larger are not a 1008 PIDs of value ``pid_max`` or larger are not allocated.
1028 1009
1029 1010
1030 ns_last_pid 1011 ns_last_pid
1031 =========== 1012 ===========
1032 1013
1033 The last pid allocated in the current (the on 1014 The last pid allocated in the current (the one task using this sysctl
1034 lives in) pid namespace. When selecting a pid 1015 lives in) pid namespace. When selecting a pid for a next task on fork
1035 kernel tries to allocate a number starting fr 1016 kernel tries to allocate a number starting from this one.
1036 1017
1037 1018
1038 powersave-nap (PPC only) 1019 powersave-nap (PPC only)
1039 ======================== 1020 ========================
1040 1021
1041 If set, Linux-PPC will use the 'nap' mode of 1022 If set, Linux-PPC will use the 'nap' mode of powersaving,
1042 otherwise the 'doze' mode will be used. 1023 otherwise the 'doze' mode will be used.
1043 1024
1044 1025
1045 ============================================= 1026 ==============================================================
1046 1027
1047 printk 1028 printk
1048 ====== 1029 ======
1049 1030
1050 The four values in printk denote: ``console_l 1031 The four values in printk denote: ``console_loglevel``,
1051 ``default_message_loglevel``, ``minimum_conso 1032 ``default_message_loglevel``, ``minimum_console_loglevel`` and
1052 ``default_console_loglevel`` respectively. 1033 ``default_console_loglevel`` respectively.
1053 1034
1054 These values influence printk() behavior when 1035 These values influence printk() behavior when printing or
1055 logging error messages. See '``man 2 syslog`` 1036 logging error messages. See '``man 2 syslog``' for more info on
1056 the different loglevels. 1037 the different loglevels.
1057 1038
1058 ======================== ==================== 1039 ======================== =====================================
1059 console_loglevel messages with a high 1040 console_loglevel messages with a higher priority than
1060 this will be printed 1041 this will be printed to the console
1061 default_message_loglevel messages without an 1042 default_message_loglevel messages without an explicit priority
1062 will be printed with 1043 will be printed with this priority
1063 minimum_console_loglevel minimum (highest) va 1044 minimum_console_loglevel minimum (highest) value to which
1064 console_loglevel can 1045 console_loglevel can be set
1065 default_console_loglevel default value for co 1046 default_console_loglevel default value for console_loglevel
1066 ======================== ==================== 1047 ======================== =====================================
1067 1048
1068 1049
1069 printk_delay 1050 printk_delay
1070 ============ 1051 ============
1071 1052
1072 Delay each printk message in ``printk_delay`` 1053 Delay each printk message in ``printk_delay`` milliseconds
1073 1054
1074 Value from 0 - 10000 is allowed. 1055 Value from 0 - 10000 is allowed.
1075 1056
1076 1057
1077 printk_ratelimit 1058 printk_ratelimit
1078 ================ 1059 ================
1079 1060
1080 Some warning messages are rate limited. ``pri 1061 Some warning messages are rate limited. ``printk_ratelimit`` specifies
1081 the minimum length of time between these mess 1062 the minimum length of time between these messages (in seconds).
1082 The default value is 5 seconds. 1063 The default value is 5 seconds.
1083 1064
1084 A value of 0 will disable rate limiting. 1065 A value of 0 will disable rate limiting.
1085 1066
1086 1067
1087 printk_ratelimit_burst 1068 printk_ratelimit_burst
1088 ====================== 1069 ======================
1089 1070
1090 While long term we enforce one message per `p 1071 While long term we enforce one message per `printk_ratelimit`_
1091 seconds, we do allow a burst of messages to p 1072 seconds, we do allow a burst of messages to pass through.
1092 ``printk_ratelimit_burst`` specifies the numb 1073 ``printk_ratelimit_burst`` specifies the number of messages we can
1093 send before ratelimiting kicks in. 1074 send before ratelimiting kicks in.
1094 1075
1095 The default value is 10 messages. 1076 The default value is 10 messages.
1096 1077
1097 1078
1098 printk_devkmsg 1079 printk_devkmsg
1099 ============== 1080 ==============
1100 1081
1101 Control the logging to ``/dev/kmsg`` from use 1082 Control the logging to ``/dev/kmsg`` from userspace:
1102 1083
1103 ========= =================================== 1084 ========= =============================================
1104 ratelimit default, ratelimited 1085 ratelimit default, ratelimited
1105 on unlimited logging to /dev/kmsg from 1086 on unlimited logging to /dev/kmsg from userspace
1106 off logging to /dev/kmsg disabled 1087 off logging to /dev/kmsg disabled
1107 ========= =================================== 1088 ========= =============================================
1108 1089
1109 The kernel command line parameter ``printk.de 1090 The kernel command line parameter ``printk.devkmsg=`` overrides this and is
1110 a one-time setting until next reboot: once se 1091 a one-time setting until next reboot: once set, it cannot be changed by
1111 this sysctl interface anymore. 1092 this sysctl interface anymore.
1112 1093
1113 ============================================= 1094 ==============================================================
1114 1095
1115 1096
1116 pty 1097 pty
1117 === 1098 ===
1118 1099
1119 See Documentation/filesystems/devpts.rst. 1100 See Documentation/filesystems/devpts.rst.
1120 1101
1121 1102
1122 random 1103 random
1123 ====== 1104 ======
1124 1105
1125 This is a directory, with the following entri 1106 This is a directory, with the following entries:
1126 1107
1127 * ``boot_id``: a UUID generated the first tim 1108 * ``boot_id``: a UUID generated the first time this is retrieved, and
1128 unvarying after that; 1109 unvarying after that;
1129 1110
1130 * ``uuid``: a UUID generated every time this 1111 * ``uuid``: a UUID generated every time this is retrieved (this can
1131 thus be used to generate UUIDs at will); 1112 thus be used to generate UUIDs at will);
1132 1113
1133 * ``entropy_avail``: the pool's entropy count 1114 * ``entropy_avail``: the pool's entropy count, in bits;
1134 1115
1135 * ``poolsize``: the entropy pool size, in bit 1116 * ``poolsize``: the entropy pool size, in bits;
1136 1117
1137 * ``urandom_min_reseed_secs``: obsolete (used 1118 * ``urandom_min_reseed_secs``: obsolete (used to determine the minimum
1138 number of seconds between urandom pool rese 1119 number of seconds between urandom pool reseeding). This file is
1139 writable for compatibility purposes, but wr 1120 writable for compatibility purposes, but writing to it has no effect
1140 on any RNG behavior; 1121 on any RNG behavior;
1141 1122
1142 * ``write_wakeup_threshold``: when the entrop 1123 * ``write_wakeup_threshold``: when the entropy count drops below this
1143 (as a number of bits), processes waiting to 1124 (as a number of bits), processes waiting to write to ``/dev/random``
1144 are woken up. This file is writable for com 1125 are woken up. This file is writable for compatibility purposes, but
1145 writing to it has no effect on any RNG beha 1126 writing to it has no effect on any RNG behavior.
1146 1127
1147 1128
1148 randomize_va_space 1129 randomize_va_space
1149 ================== 1130 ==================
1150 1131
1151 This option can be used to select the type of 1132 This option can be used to select the type of process address
1152 space randomization that is used in the syste 1133 space randomization that is used in the system, for architectures
1153 that support this feature. 1134 that support this feature.
1154 1135
1155 == ========================================= 1136 == ===========================================================================
1156 0 Turn the process address space randomizat 1137 0 Turn the process address space randomization off. This is the
1157 default for architectures that do not sup 1138 default for architectures that do not support this feature anyways,
1158 and kernels that are booted with the "nor 1139 and kernels that are booted with the "norandmaps" parameter.
1159 1140
1160 1 Make the addresses of mmap base, stack an 1141 1 Make the addresses of mmap base, stack and VDSO page randomized.
1161 This, among other things, implies that sh 1142 This, among other things, implies that shared libraries will be
1162 loaded to random addresses. Also for PIE 1143 loaded to random addresses. Also for PIE-linked binaries, the
1163 location of code start is randomized. Th 1144 location of code start is randomized. This is the default if the
1164 ``CONFIG_COMPAT_BRK`` option is enabled. 1145 ``CONFIG_COMPAT_BRK`` option is enabled.
1165 1146
1166 2 Additionally enable heap randomization. 1147 2 Additionally enable heap randomization. This is the default if
1167 ``CONFIG_COMPAT_BRK`` is disabled. 1148 ``CONFIG_COMPAT_BRK`` is disabled.
1168 1149
1169 There are a few legacy applications out t 1150 There are a few legacy applications out there (such as some ancient
1170 versions of libc.so.5 from 1996) that ass 1151 versions of libc.so.5 from 1996) that assume that brk area starts
1171 just after the end of the code+bss. Thes 1152 just after the end of the code+bss. These applications break when
1172 start of the brk area is randomized. The 1153 start of the brk area is randomized. There are however no known
1173 non-legacy applications that would be bro 1154 non-legacy applications that would be broken this way, so for most
1174 systems it is safe to choose full randomi 1155 systems it is safe to choose full randomization.
1175 1156
1176 Systems with ancient and/or broken binari 1157 Systems with ancient and/or broken binaries should be configured
1177 with ``CONFIG_COMPAT_BRK`` enabled, which 1158 with ``CONFIG_COMPAT_BRK`` enabled, which excludes the heap from process
1178 address space randomization. 1159 address space randomization.
1179 == ========================================= 1160 == ===========================================================================
1180 1161
1181 1162
1182 real-root-dev 1163 real-root-dev
1183 ============= 1164 =============
1184 1165
1185 See Documentation/admin-guide/initrd.rst. 1166 See Documentation/admin-guide/initrd.rst.
1186 1167
1187 1168
1188 reboot-cmd (SPARC only) 1169 reboot-cmd (SPARC only)
1189 ======================= 1170 =======================
1190 1171
1191 ??? This seems to be a way to give an argumen 1172 ??? This seems to be a way to give an argument to the Sparc
1192 ROM/Flash boot loader. Maybe to tell it what 1173 ROM/Flash boot loader. Maybe to tell it what to do after
1193 rebooting. ??? 1174 rebooting. ???
1194 1175
1195 1176
1196 sched_energy_aware 1177 sched_energy_aware
1197 ================== 1178 ==================
1198 1179
1199 Enables/disables Energy Aware Scheduling (EAS 1180 Enables/disables Energy Aware Scheduling (EAS). EAS starts
1200 automatically on platforms where it can run ( 1181 automatically on platforms where it can run (that is,
1201 platforms with asymmetric CPU topologies and 1182 platforms with asymmetric CPU topologies and having an Energy
1202 Model available). If your platform happens to 1183 Model available). If your platform happens to meet the
1203 requirements for EAS but you do not want to u 1184 requirements for EAS but you do not want to use it, change
1204 this value to 0. On Non-EAS platforms, write !! 1185 this value to 0.
1205 read doesn't return anything. <<
1206 1186
1207 task_delayacct 1187 task_delayacct
1208 =============== 1188 ===============
1209 1189
1210 Enables/disables task delay accounting (see 1190 Enables/disables task delay accounting (see
1211 Documentation/accounting/delay-accounting.rst 1191 Documentation/accounting/delay-accounting.rst. Enabling this feature incurs
1212 a small amount of overhead in the scheduler b 1192 a small amount of overhead in the scheduler but is useful for debugging
1213 and performance tuning. It is required by som 1193 and performance tuning. It is required by some tools such as iotop.
1214 1194
1215 sched_schedstats 1195 sched_schedstats
1216 ================ 1196 ================
1217 1197
1218 Enables/disables scheduler statistics. Enabli 1198 Enables/disables scheduler statistics. Enabling this feature
1219 incurs a small amount of overhead in the sche 1199 incurs a small amount of overhead in the scheduler but is
1220 useful for debugging and performance tuning. 1200 useful for debugging and performance tuning.
1221 1201
1222 sched_util_clamp_min 1202 sched_util_clamp_min
1223 ==================== 1203 ====================
1224 1204
1225 Max allowed *minimum* utilization. 1205 Max allowed *minimum* utilization.
1226 1206
1227 Default value is 1024, which is the maximum p 1207 Default value is 1024, which is the maximum possible value.
1228 1208
1229 It means that any requested uclamp.min value 1209 It means that any requested uclamp.min value cannot be greater than
1230 sched_util_clamp_min, i.e., it is restricted 1210 sched_util_clamp_min, i.e., it is restricted to the range
1231 [0:sched_util_clamp_min]. 1211 [0:sched_util_clamp_min].
1232 1212
1233 sched_util_clamp_max 1213 sched_util_clamp_max
1234 ==================== 1214 ====================
1235 1215
1236 Max allowed *maximum* utilization. 1216 Max allowed *maximum* utilization.
1237 1217
1238 Default value is 1024, which is the maximum p 1218 Default value is 1024, which is the maximum possible value.
1239 1219
1240 It means that any requested uclamp.max value 1220 It means that any requested uclamp.max value cannot be greater than
1241 sched_util_clamp_max, i.e., it is restricted 1221 sched_util_clamp_max, i.e., it is restricted to the range
1242 [0:sched_util_clamp_max]. 1222 [0:sched_util_clamp_max].
1243 1223
1244 sched_util_clamp_min_rt_default 1224 sched_util_clamp_min_rt_default
1245 =============================== 1225 ===============================
1246 1226
1247 By default Linux is tuned for performance. Wh 1227 By default Linux is tuned for performance. Which means that RT tasks always run
1248 at the highest frequency and most capable (hi 1228 at the highest frequency and most capable (highest capacity) CPU (in
1249 heterogeneous systems). 1229 heterogeneous systems).
1250 1230
1251 Uclamp achieves this by setting the requested 1231 Uclamp achieves this by setting the requested uclamp.min of all RT tasks to
1252 1024 by default, which effectively boosts the 1232 1024 by default, which effectively boosts the tasks to run at the highest
1253 frequency and biases them to run on the bigge 1233 frequency and biases them to run on the biggest CPU.
1254 1234
1255 This knob allows admins to change the default 1235 This knob allows admins to change the default behavior when uclamp is being
1256 used. In battery powered devices particularly 1236 used. In battery powered devices particularly, running at the maximum
1257 capacity and frequency will increase energy c 1237 capacity and frequency will increase energy consumption and shorten the battery
1258 life. 1238 life.
1259 1239
1260 This knob is only effective for RT tasks whic 1240 This knob is only effective for RT tasks which the user hasn't modified their
1261 requested uclamp.min value via sched_setattr( 1241 requested uclamp.min value via sched_setattr() syscall.
1262 1242
1263 This knob will not escape the range constrain 1243 This knob will not escape the range constraint imposed by sched_util_clamp_min
1264 defined above. 1244 defined above.
1265 1245
1266 For example if 1246 For example if
1267 1247
1268 sched_util_clamp_min_rt_default = 800 1248 sched_util_clamp_min_rt_default = 800
1269 sched_util_clamp_min = 600 1249 sched_util_clamp_min = 600
1270 1250
1271 Then the boost will be clamped to 600 because 1251 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 1252 range of [0:600]. This could happen for instance if a powersave mode will
1273 restrict all boosts temporarily by modifying 1253 restrict all boosts temporarily by modifying sched_util_clamp_min. As soon as
1274 this restriction is lifted, the requested sch 1254 this restriction is lifted, the requested sched_util_clamp_min_rt_default
1275 will take effect. 1255 will take effect.
1276 1256
1277 seccomp 1257 seccomp
1278 ======= 1258 =======
1279 1259
1280 See Documentation/userspace-api/seccomp_filte 1260 See Documentation/userspace-api/seccomp_filter.rst.
1281 1261
1282 1262
1283 sg-big-buff 1263 sg-big-buff
1284 =========== 1264 ===========
1285 1265
1286 This file shows the size of the generic SCSI 1266 This file shows the size of the generic SCSI (sg) buffer.
1287 You can't tune it just yet, but you could cha 1267 You can't tune it just yet, but you could change it on
1288 compile time by editing ``include/scsi/sg.h`` 1268 compile time by editing ``include/scsi/sg.h`` and changing
1289 the value of ``SG_BIG_BUFF``. 1269 the value of ``SG_BIG_BUFF``.
1290 1270
1291 There shouldn't be any reason to change this 1271 There shouldn't be any reason to change this value. If
1292 you can come up with one, you probably know w 1272 you can come up with one, you probably know what you
1293 are doing anyway :) 1273 are doing anyway :)
1294 1274
1295 1275
1296 shmall 1276 shmall
1297 ====== 1277 ======
1298 1278
1299 This parameter sets the total amount of share !! 1279 This parameter sets the total amount of shared memory pages that
1300 inside ipc namespace. The shared memory pages !! 1280 can be used system wide. Hence, ``shmall`` should always be at least
1301 namespace separately and is not inherited. He !! 1281 ``ceil(shmmax/PAGE_SIZE)``.
1302 least ``ceil(shmmax/PAGE_SIZE)``. <<
1303 1282
1304 If you are not sure what the default ``PAGE_S 1283 If you are not sure what the default ``PAGE_SIZE`` is on your Linux
1305 system, you can run the following command:: 1284 system, you can run the following command::
1306 1285
1307 # getconf PAGE_SIZE 1286 # getconf PAGE_SIZE
1308 1287
1309 To reduce or disable the ability to allocate <<
1310 new ipc namespace, set this parameter to the <<
1311 creation of a new ipc namespace in the curren <<
1312 be used. <<
1313 1288
1314 shmmax 1289 shmmax
1315 ====== 1290 ======
1316 1291
1317 This value can be used to query and set the r 1292 This value can be used to query and set the run time limit
1318 on the maximum shared memory segment size tha 1293 on the maximum shared memory segment size that can be created.
1319 Shared memory segments up to 1Gb are now supp 1294 Shared memory segments up to 1Gb are now supported in the
1320 kernel. This value defaults to ``SHMMAX``. 1295 kernel. This value defaults to ``SHMMAX``.
1321 1296
1322 1297
1323 shmmni 1298 shmmni
1324 ====== 1299 ======
1325 1300
1326 This value determines the maximum number of s 1301 This value determines the maximum number of shared memory segments.
1327 4096 by default (``SHMMNI``). 1302 4096 by default (``SHMMNI``).
1328 1303
1329 1304
1330 shm_rmid_forced 1305 shm_rmid_forced
1331 =============== 1306 ===============
1332 1307
1333 Linux lets you set resource limits, including 1308 Linux lets you set resource limits, including how much memory one
1334 process can consume, via ``setrlimit(2)``. U 1309 process can consume, via ``setrlimit(2)``. Unfortunately, shared memory
1335 segments are allowed to exist without associa 1310 segments are allowed to exist without association with any process, and
1336 thus might not be counted against any resourc 1311 thus might not be counted against any resource limits. If enabled,
1337 shared memory segments are automatically dest 1312 shared memory segments are automatically destroyed when their attach
1338 count becomes zero after a detach or a proces 1313 count becomes zero after a detach or a process termination. It will
1339 also destroy segments that were created, but 1314 also destroy segments that were created, but never attached to, on exit
1340 from the process. The only use left for ``IP 1315 from the process. The only use left for ``IPC_RMID`` is to immediately
1341 destroy an unattached segment. Of course, th 1316 destroy an unattached segment. Of course, this breaks the way things are
1342 defined, so some applications might stop work 1317 defined, so some applications might stop working. Note that this
1343 feature will do you no good unless you also c 1318 feature will do you no good unless you also configure your resource
1344 limits (in particular, ``RLIMIT_AS`` and ``RL 1319 limits (in particular, ``RLIMIT_AS`` and ``RLIMIT_NPROC``). Most systems don't
1345 need this. 1320 need this.
1346 1321
1347 Note that if you change this from 0 to 1, alr 1322 Note that if you change this from 0 to 1, already created segments
1348 without users and with a dead originative pro 1323 without users and with a dead originative process will be destroyed.
1349 1324
1350 1325
1351 sysctl_writes_strict 1326 sysctl_writes_strict
1352 ==================== 1327 ====================
1353 1328
1354 Control how file position affects the behavio 1329 Control how file position affects the behavior of updating sysctl values
1355 via the ``/proc/sys`` interface: 1330 via the ``/proc/sys`` interface:
1356 1331
1357 == ====================================== 1332 == ======================================================================
1358 -1 Legacy per-write sysctl value handling 1333 -1 Legacy per-write sysctl value handling, with no printk warnings.
1359 Each write syscall must fully contain 1334 Each write syscall must fully contain the sysctl value to be
1360 written, and multiple writes on the sa 1335 written, and multiple writes on the same sysctl file descriptor
1361 will rewrite the sysctl value, regardl 1336 will rewrite the sysctl value, regardless of file position.
1362 0 Same behavior as above, but warn about 1337 0 Same behavior as above, but warn about processes that perform writes
1363 to a sysctl file descriptor when the f 1338 to a sysctl file descriptor when the file position is not 0.
1364 1 (default) Respect file position when w 1339 1 (default) Respect file position when writing sysctl strings. Multiple
1365 writes will append to the sysctl value 1340 writes will append to the sysctl value buffer. Anything past the max
1366 length of the sysctl value buffer will 1341 length of the sysctl value buffer will be ignored. Writes to numeric
1367 sysctl entries must always be at file 1342 sysctl entries must always be at file position 0 and the value must
1368 be fully contained in the buffer sent 1343 be fully contained in the buffer sent in the write syscall.
1369 == ====================================== 1344 == ======================================================================
1370 1345
1371 1346
1372 softlockup_all_cpu_backtrace 1347 softlockup_all_cpu_backtrace
1373 ============================ 1348 ============================
1374 1349
1375 This value controls the soft lockup detector 1350 This value controls the soft lockup detector thread's behavior
1376 when a soft lockup condition is detected as t 1351 when a soft lockup condition is detected as to whether or not
1377 to gather further debug information. If enabl 1352 to gather further debug information. If enabled, each cpu will
1378 be issued an NMI and instructed to capture st 1353 be issued an NMI and instructed to capture stack trace.
1379 1354
1380 This feature is only applicable for architect 1355 This feature is only applicable for architectures which support
1381 NMI. 1356 NMI.
1382 1357
1383 = =========================================== 1358 = ============================================
1384 0 Do nothing. This is the default behavior. 1359 0 Do nothing. This is the default behavior.
1385 1 On detection capture more debug information 1360 1 On detection capture more debug information.
1386 = =========================================== 1361 = ============================================
1387 1362
1388 1363
1389 softlockup_panic 1364 softlockup_panic
1390 ================= 1365 =================
1391 1366
1392 This parameter can be used to control whether 1367 This parameter can be used to control whether the kernel panics
1393 when a soft lockup is detected. 1368 when a soft lockup is detected.
1394 1369
1395 = =========================================== 1370 = ============================================
1396 0 Don't panic on soft lockup. 1371 0 Don't panic on soft lockup.
1397 1 Panic on soft lockup. 1372 1 Panic on soft lockup.
1398 = =========================================== 1373 = ============================================
1399 1374
1400 This can also be set using the softlockup_pan 1375 This can also be set using the softlockup_panic kernel parameter.
1401 1376
1402 1377
1403 soft_watchdog 1378 soft_watchdog
1404 ============= 1379 =============
1405 1380
1406 This parameter can be used to control the sof 1381 This parameter can be used to control the soft lockup detector.
1407 1382
1408 = ================================= 1383 = =================================
1409 0 Disable the soft lockup detector. 1384 0 Disable the soft lockup detector.
1410 1 Enable the soft lockup detector. 1385 1 Enable the soft lockup detector.
1411 = ================================= 1386 = =================================
1412 1387
1413 The soft lockup detector monitors CPUs for th 1388 The soft lockup detector monitors CPUs for threads that are hogging the CPUs
1414 without rescheduling voluntarily, and thus pr 1389 without rescheduling voluntarily, and thus prevent the 'migration/N' threads
1415 from running, causing the watchdog work fail 1390 from running, causing the watchdog work fail to execute. The mechanism depends
1416 on the CPUs ability to respond to timer inter 1391 on the CPUs ability to respond to timer interrupts which are needed for the
1417 watchdog work to be queued by the watchdog ti 1392 watchdog work to be queued by the watchdog timer function, otherwise the NMI
1418 watchdog — if enabled — can detect a hard 1393 watchdog — if enabled — can detect a hard lockup condition.
1419 1394
1420 1395
1421 split_lock_mitigate (x86 only) 1396 split_lock_mitigate (x86 only)
1422 ============================== 1397 ==============================
1423 1398
1424 On x86, each "split lock" imposes a system-wi 1399 On x86, each "split lock" imposes a system-wide performance penalty. On larger
1425 systems, large numbers of split locks from un 1400 systems, large numbers of split locks from unprivileged users can result in
1426 denials of service to well-behaved and potent 1401 denials of service to well-behaved and potentially more important users.
1427 1402
1428 The kernel mitigates these bad users by detec 1403 The kernel mitigates these bad users by detecting split locks and imposing
1429 penalties: forcing them to wait and only allo 1404 penalties: forcing them to wait and only allowing one core to execute split
1430 locks at a time. 1405 locks at a time.
1431 1406
1432 These mitigations can make those bad applicat 1407 These mitigations can make those bad applications unbearably slow. Setting
1433 split_lock_mitigate=0 may restore some applic 1408 split_lock_mitigate=0 may restore some application performance, but will also
1434 increase system exposure to denial of service 1409 increase system exposure to denial of service attacks from split lock users.
1435 1410
1436 = =========================================== 1411 = ===================================================================
1437 0 Disable the mitigation mode - just warns th 1412 0 Disable the mitigation mode - just warns the split lock on kernel log
1438 and exposes the system to denials of servic 1413 and exposes the system to denials of service from the split lockers.
1439 1 Enable the mitigation mode (this is the def 1414 1 Enable the mitigation mode (this is the default) - penalizes the split
1440 lockers with intentional performance degrad 1415 lockers with intentional performance degradation.
1441 = =========================================== 1416 = ===================================================================
1442 1417
1443 1418
1444 stack_erasing 1419 stack_erasing
1445 ============= 1420 =============
1446 1421
1447 This parameter can be used to control kernel 1422 This parameter can be used to control kernel stack erasing at the end
1448 of syscalls for kernels built with ``CONFIG_G 1423 of syscalls for kernels built with ``CONFIG_GCC_PLUGIN_STACKLEAK``.
1449 1424
1450 That erasing reduces the information which ke 1425 That erasing reduces the information which kernel stack leak bugs
1451 can reveal and blocks some uninitialized stac 1426 can reveal and blocks some uninitialized stack variable attacks.
1452 The tradeoff is the performance impact: on a 1427 The tradeoff is the performance impact: on a single CPU system kernel
1453 compilation sees a 1% slowdown, other systems 1428 compilation sees a 1% slowdown, other systems and workloads may vary.
1454 1429
1455 = =========================================== 1430 = ====================================================================
1456 0 Kernel stack erasing is disabled, STACKLEAK 1431 0 Kernel stack erasing is disabled, STACKLEAK_METRICS are not updated.
1457 1 Kernel stack erasing is enabled (default), 1432 1 Kernel stack erasing is enabled (default), it is performed before
1458 returning to the userspace at the end of sy 1433 returning to the userspace at the end of syscalls.
1459 = =========================================== 1434 = ====================================================================
1460 1435
1461 1436
1462 stop-a (SPARC only) 1437 stop-a (SPARC only)
1463 =================== 1438 ===================
1464 1439
1465 Controls Stop-A: 1440 Controls Stop-A:
1466 1441
1467 = ==================================== 1442 = ====================================
1468 0 Stop-A has no effect. 1443 0 Stop-A has no effect.
1469 1 Stop-A breaks to the PROM (default). 1444 1 Stop-A breaks to the PROM (default).
1470 = ==================================== 1445 = ====================================
1471 1446
1472 Stop-A is always enabled on a panic, so that 1447 Stop-A is always enabled on a panic, so that the user can return to
1473 the boot PROM. 1448 the boot PROM.
1474 1449
1475 1450
1476 sysrq 1451 sysrq
1477 ===== 1452 =====
1478 1453
1479 See Documentation/admin-guide/sysrq.rst. 1454 See Documentation/admin-guide/sysrq.rst.
1480 1455
1481 1456
1482 tainted 1457 tainted
1483 ======= 1458 =======
1484 1459
1485 Non-zero if the kernel has been tainted. Nume 1460 Non-zero if the kernel has been tainted. Numeric values, which can be
1486 ORed together. The letters are seen in "Taint 1461 ORed together. The letters are seen in "Tainted" line of Oops reports.
1487 1462
1488 ====== ===== ============================== 1463 ====== ===== ==============================================================
1489 1 `(P)` proprietary module was loaded 1464 1 `(P)` proprietary module was loaded
1490 2 `(F)` module was force loaded 1465 2 `(F)` module was force loaded
1491 4 `(S)` kernel running on an out of sp 1466 4 `(S)` kernel running on an out of specification system
1492 8 `(R)` module was force unloaded 1467 8 `(R)` module was force unloaded
1493 16 `(M)` processor reported a Machine C 1468 16 `(M)` processor reported a Machine Check Exception (MCE)
1494 32 `(B)` bad page referenced or some un 1469 32 `(B)` bad page referenced or some unexpected page flags
1495 64 `(U)` taint requested by userspace a 1470 64 `(U)` taint requested by userspace application
1496 128 `(D)` kernel died recently, i.e. the 1471 128 `(D)` kernel died recently, i.e. there was an OOPS or BUG
1497 256 `(A)` an ACPI table was overridden b 1472 256 `(A)` an ACPI table was overridden by user
1498 512 `(W)` kernel issued warning 1473 512 `(W)` kernel issued warning
1499 1024 `(C)` staging driver was loaded 1474 1024 `(C)` staging driver was loaded
1500 2048 `(I)` workaround for bug in platform 1475 2048 `(I)` workaround for bug in platform firmware applied
1501 4096 `(O)` externally-built ("out-of-tree 1476 4096 `(O)` externally-built ("out-of-tree") module was loaded
1502 8192 `(E)` unsigned module was loaded 1477 8192 `(E)` unsigned module was loaded
1503 16384 `(L)` soft lockup occurred 1478 16384 `(L)` soft lockup occurred
1504 32768 `(K)` kernel has been live patched 1479 32768 `(K)` kernel has been live patched
1505 65536 `(X)` Auxiliary taint, defined and u 1480 65536 `(X)` Auxiliary taint, defined and used by for distros
1506 131072 `(T)` The kernel was built with the 1481 131072 `(T)` The kernel was built with the struct randomization plugin
1507 ====== ===== ============================== 1482 ====== ===== ==============================================================
1508 1483
1509 See Documentation/admin-guide/tainted-kernels 1484 See Documentation/admin-guide/tainted-kernels.rst for more information.
1510 1485
1511 Note: 1486 Note:
1512 writes to this sysctl interface will fail w 1487 writes to this sysctl interface will fail with ``EINVAL`` if the kernel is
1513 booted with the command line option ``panic 1488 booted with the command line option ``panic_on_taint=<bitmask>,nousertaint``
1514 and any of the ORed together values being w 1489 and any of the ORed together values being written to ``tainted`` match with
1515 the bitmask declared on panic_on_taint. 1490 the bitmask declared on panic_on_taint.
1516 See Documentation/admin-guide/kernel-parame 1491 See Documentation/admin-guide/kernel-parameters.rst for more details on
1517 that particular kernel command line option 1492 that particular kernel command line option and its optional
1518 ``nousertaint`` switch. 1493 ``nousertaint`` switch.
1519 1494
1520 threads-max 1495 threads-max
1521 =========== 1496 ===========
1522 1497
1523 This value controls the maximum number of thr 1498 This value controls the maximum number of threads that can be created
1524 using ``fork()``. 1499 using ``fork()``.
1525 1500
1526 During initialization the kernel sets this va 1501 During initialization the kernel sets this value such that even if the
1527 maximum number of threads is created, the thr 1502 maximum number of threads is created, the thread structures occupy only
1528 a part (1/8th) of the available RAM pages. 1503 a part (1/8th) of the available RAM pages.
1529 1504
1530 The minimum value that can be written to ``th 1505 The minimum value that can be written to ``threads-max`` is 1.
1531 1506
1532 The maximum value that can be written to ``th 1507 The maximum value that can be written to ``threads-max`` is given by the
1533 constant ``FUTEX_TID_MASK`` (0x3fffffff). 1508 constant ``FUTEX_TID_MASK`` (0x3fffffff).
1534 1509
1535 If a value outside of this range is written t 1510 If a value outside of this range is written to ``threads-max`` an
1536 ``EINVAL`` error occurs. 1511 ``EINVAL`` error occurs.
1537 1512
1538 1513
1539 traceoff_on_warning 1514 traceoff_on_warning
1540 =================== 1515 ===================
1541 1516
1542 When set, disables tracing (see Documentation 1517 When set, disables tracing (see Documentation/trace/ftrace.rst) when a
1543 ``WARN()`` is hit. 1518 ``WARN()`` is hit.
1544 1519
1545 1520
1546 tracepoint_printk 1521 tracepoint_printk
1547 ================= 1522 =================
1548 1523
1549 When tracepoints are sent to printk() (enable 1524 When tracepoints are sent to printk() (enabled by the ``tp_printk``
1550 boot parameter), this entry provides runtime 1525 boot parameter), this entry provides runtime control::
1551 1526
1552 echo 0 > /proc/sys/kernel/tracepoint_prin 1527 echo 0 > /proc/sys/kernel/tracepoint_printk
1553 1528
1554 will stop tracepoints from being sent to prin 1529 will stop tracepoints from being sent to printk(), and::
1555 1530
1556 echo 1 > /proc/sys/kernel/tracepoint_prin 1531 echo 1 > /proc/sys/kernel/tracepoint_printk
1557 1532
1558 will send them to printk() again. 1533 will send them to printk() again.
1559 1534
1560 This only works if the kernel was booted with 1535 This only works if the kernel was booted with ``tp_printk`` enabled.
1561 1536
1562 See Documentation/admin-guide/kernel-paramete 1537 See Documentation/admin-guide/kernel-parameters.rst and
1563 Documentation/trace/boottime-trace.rst. 1538 Documentation/trace/boottime-trace.rst.
>> 1539
>> 1540
>> 1541 .. _unaligned-dump-stack:
>> 1542
>> 1543 unaligned-dump-stack (ia64)
>> 1544 ===========================
>> 1545
>> 1546 When logging unaligned accesses, controls whether the stack is
>> 1547 dumped.
>> 1548
>> 1549 = ===================================================
>> 1550 0 Do not dump the stack. This is the default setting.
>> 1551 1 Dump the stack.
>> 1552 = ===================================================
>> 1553
>> 1554 See also `ignore-unaligned-usertrap`_.
1564 1555
1565 1556
1566 unaligned-trap 1557 unaligned-trap
1567 ============== 1558 ==============
1568 1559
1569 On architectures where unaligned accesses cau 1560 On architectures where unaligned accesses cause traps, and where this
1570 feature is supported (``CONFIG_SYSCTL_ARCH_UN 1561 feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_ALLOW``; currently,
1571 ``arc``, ``parisc`` and ``loongarch``), contr 1562 ``arc``, ``parisc`` and ``loongarch``), controls whether unaligned traps
1572 are caught and emulated (instead of failing). 1563 are caught and emulated (instead of failing).
1573 1564
1574 = =========================================== 1565 = ========================================================
1575 0 Do not emulate unaligned accesses. 1566 0 Do not emulate unaligned accesses.
1576 1 Emulate unaligned accesses. This is the def 1567 1 Emulate unaligned accesses. This is the default setting.
1577 = =========================================== 1568 = ========================================================
1578 1569
1579 See also `ignore-unaligned-usertrap`_. 1570 See also `ignore-unaligned-usertrap`_.
1580 1571
1581 1572
1582 unknown_nmi_panic 1573 unknown_nmi_panic
1583 ================= 1574 =================
1584 1575
1585 The value in this file affects behavior of ha 1576 The value in this file affects behavior of handling NMI. When the
1586 value is non-zero, unknown NMI is trapped and 1577 value is non-zero, unknown NMI is trapped and then panic occurs. At
1587 that time, kernel debugging information is di 1578 that time, kernel debugging information is displayed on console.
1588 1579
1589 NMI switch that most IA32 servers have fires 1580 NMI switch that most IA32 servers have fires unknown NMI up, for
1590 example. If a system hangs up, try pressing 1581 example. If a system hangs up, try pressing the NMI switch.
1591 1582
1592 1583
1593 unprivileged_bpf_disabled 1584 unprivileged_bpf_disabled
1594 ========================= 1585 =========================
1595 1586
1596 Writing 1 to this entry will disable unprivil 1587 Writing 1 to this entry will disable unprivileged calls to ``bpf()``;
1597 once disabled, calling ``bpf()`` without ``CA 1588 once disabled, calling ``bpf()`` without ``CAP_SYS_ADMIN`` or ``CAP_BPF``
1598 will return ``-EPERM``. Once set to 1, this c 1589 will return ``-EPERM``. Once set to 1, this can't be cleared from the
1599 running kernel anymore. 1590 running kernel anymore.
1600 1591
1601 Writing 2 to this entry will also disable unp 1592 Writing 2 to this entry will also disable unprivileged calls to ``bpf()``,
1602 however, an admin can still change this setti 1593 however, an admin can still change this setting later on, if needed, by
1603 writing 0 or 1 to this entry. 1594 writing 0 or 1 to this entry.
1604 1595
1605 If ``BPF_UNPRIV_DEFAULT_OFF`` is enabled in t 1596 If ``BPF_UNPRIV_DEFAULT_OFF`` is enabled in the kernel config, then this
1606 entry will default to 2 instead of 0. 1597 entry will default to 2 instead of 0.
1607 1598
1608 = =========================================== 1599 = =============================================================
1609 0 Unprivileged calls to ``bpf()`` are enabled 1600 0 Unprivileged calls to ``bpf()`` are enabled
1610 1 Unprivileged calls to ``bpf()`` are disable 1601 1 Unprivileged calls to ``bpf()`` are disabled without recovery
1611 2 Unprivileged calls to ``bpf()`` are disable 1602 2 Unprivileged calls to ``bpf()`` are disabled
1612 = =========================================== 1603 = =============================================================
1613 1604
1614 1605
1615 warn_limit 1606 warn_limit
1616 ========== 1607 ==========
1617 1608
1618 Number of kernel warnings after which the ker 1609 Number of kernel warnings after which the kernel should panic when
1619 ``panic_on_warn`` is not set. Setting this to 1610 ``panic_on_warn`` is not set. Setting this to 0 disables checking
1620 the warning count. Setting this to 1 has the 1611 the warning count. Setting this to 1 has the same effect as setting
1621 ``panic_on_warn=1``. The default value is 0. 1612 ``panic_on_warn=1``. The default value is 0.
1622 1613
1623 1614
1624 watchdog 1615 watchdog
1625 ======== 1616 ========
1626 1617
1627 This parameter can be used to disable or enab 1618 This parameter can be used to disable or enable the soft lockup detector
1628 *and* the NMI watchdog (i.e. the hard lockup 1619 *and* the NMI watchdog (i.e. the hard lockup detector) at the same time.
1629 1620
1630 = ============================== 1621 = ==============================
1631 0 Disable both lockup detectors. 1622 0 Disable both lockup detectors.
1632 1 Enable both lockup detectors. 1623 1 Enable both lockup detectors.
1633 = ============================== 1624 = ==============================
1634 1625
1635 The soft lockup detector and the NMI watchdog 1626 The soft lockup detector and the NMI watchdog can also be disabled or
1636 enabled individually, using the ``soft_watchd 1627 enabled individually, using the ``soft_watchdog`` and ``nmi_watchdog``
1637 parameters. 1628 parameters.
1638 If the ``watchdog`` parameter is read, for ex 1629 If the ``watchdog`` parameter is read, for example by executing::
1639 1630
1640 cat /proc/sys/kernel/watchdog 1631 cat /proc/sys/kernel/watchdog
1641 1632
1642 the output of this command (0 or 1) shows the 1633 the output of this command (0 or 1) shows the logical OR of
1643 ``soft_watchdog`` and ``nmi_watchdog``. 1634 ``soft_watchdog`` and ``nmi_watchdog``.
1644 1635
1645 1636
1646 watchdog_cpumask 1637 watchdog_cpumask
1647 ================ 1638 ================
1648 1639
1649 This value can be used to control on which cp 1640 This value can be used to control on which cpus the watchdog may run.
1650 The default cpumask is all possible cores, bu 1641 The default cpumask is all possible cores, but if ``NO_HZ_FULL`` is
1651 enabled in the kernel config, and cores are s 1642 enabled in the kernel config, and cores are specified with the
1652 ``nohz_full=`` boot argument, those cores are 1643 ``nohz_full=`` boot argument, those cores are excluded by default.
1653 Offline cores can be included in this mask, a 1644 Offline cores can be included in this mask, and if the core is later
1654 brought online, the watchdog will be started 1645 brought online, the watchdog will be started based on the mask value.
1655 1646
1656 Typically this value would only be touched in 1647 Typically this value would only be touched in the ``nohz_full`` case
1657 to re-enable cores that by default were not r 1648 to re-enable cores that by default were not running the watchdog,
1658 if a kernel lockup was suspected on those cor 1649 if a kernel lockup was suspected on those cores.
1659 1650
1660 The argument value is the standard cpulist fo 1651 The argument value is the standard cpulist format for cpumasks,
1661 so for example to enable the watchdog on core 1652 so for example to enable the watchdog on cores 0, 2, 3, and 4 you
1662 might say:: 1653 might say::
1663 1654
1664 echo 0,2-4 > /proc/sys/kernel/watchdog_cpum 1655 echo 0,2-4 > /proc/sys/kernel/watchdog_cpumask
1665 1656
1666 1657
1667 watchdog_thresh 1658 watchdog_thresh
1668 =============== 1659 ===============
1669 1660
1670 This value can be used to control the frequen 1661 This value can be used to control the frequency of hrtimer and NMI
1671 events and the soft and hard lockup threshold 1662 events and the soft and hard lockup thresholds. The default threshold
1672 is 10 seconds. 1663 is 10 seconds.
1673 1664
1674 The softlockup threshold is (``2 * watchdog_t 1665 The softlockup threshold is (``2 * watchdog_thresh``). Setting this
1675 tunable to zero will disable lockup detection 1666 tunable to zero will disable lockup detection altogether.
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