1 Tainted kernels
2 ---------------
3
4 The kernel will mark itself as 'tainted' when
5 relevant later when investigating problems. Do
6 most of the time it's not a problem to run a t
7 mainly of interest once someone wants to inves
8 cause might be the event that got the kernel t
9 from tainted kernels will often be ignored by
10 problems with an untainted kernel.
11
12 Note the kernel will remain tainted even after
13 (i.e. unload a proprietary kernel module), to
14 trustworthy. That's also why the kernel will p
15 notices an internal problem (a 'kernel bug'),
16 ('kernel oops') or a non-recoverable error ('k
17 information about this to the logs ``dmesg`` o
18 check the tainted state at runtime through a f
19
20
21 Tainted flag in bugs, oops or panics messages
22 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
23
24 You find the tainted state near the top in a l
25 why the kernel was tainted is shown after the
26 name of the command ('Comm:') that triggered t
27
28 BUG: unable to handle kernel NULL poin
29 Oops: 0002 [#1] SMP PTI
30 CPU: 0 PID: 4424 Comm: insmod Tainted:
31 Hardware name: Red Hat KVM, BIOS 0.5.1
32 RIP: 0010:my_oops_init+0x13/0x1000 [kp
33 [...]
34
35 You'll find a 'Not tainted: ' there if the ker
36 time of the event; if it was, then it will pri
37 either letters or blanks. In the example above
38
39 Tainted: P W O
40
41 The meaning of those characters is explained i
42 the kernel got tainted earlier because a propr
43 a warning occurred (``W``), and an externally-
44 To decode other letters use the table below.
45
46
47 Decoding tainted state at runtime
48 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
49
50 At runtime, you can query the tainted state by
51 ``cat /proc/sys/kernel/tainted``. If that retu
52 tainted; any other number indicates the reason
53 decode that number is the script ``tools/debug
54 distribution might ship as part of a package c
55 ``kernel-tools``; if it doesn't, you can downl
56 `git.kernel.org <https://git.kernel.org/pub/sc
57 and execute it with ``sh kernel-chktaint``, wh
58 this on the machine that had the statements in
59
60 Kernel is Tainted for following reason
61 * Proprietary module was loaded (#0)
62 * Kernel issued warning (#9)
63 * Externally-built ('out-of-tree') mo
64 See Documentation/admin-guide/tainted-
65 https://www.kernel.org/doc/html/lates
66 a more details explanation of the var
67 Raw taint value as int/string: 4609/'P
68
69 You can try to decode the number yourself. Tha
70 reason that got your kernel tainted, as in thi
71 with the table below. If there were multiple r
72 number, as it is a bitfield, where each bit in
73 a particular type of taint. It's best to leave
74 script, but if you need something quick you ca
75 which bits are set::
76
77 $ for i in $(seq 18); do echo $(($i-1)
78
79 Table for decoding tainted state
80 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
81
82 === === ====== ============================
83 Bit Log Number Reason that got the kernel t
84 === === ====== ============================
85 0 G/P 1 proprietary module was loade
86 1 _/F 2 module was force loaded
87 2 _/S 4 kernel running on an out of
88 3 _/R 8 module was force unloaded
89 4 _/M 16 processor reported a Machine
90 5 _/B 32 bad page referenced or some
91 6 _/U 64 taint requested by userspace
92 7 _/D 128 kernel died recently, i.e. t
93 8 _/A 256 ACPI table overridden by use
94 9 _/W 512 kernel issued warning
95 10 _/C 1024 staging driver was loaded
96 11 _/I 2048 workaround for bug in platfo
97 12 _/O 4096 externally-built ("out-of-tr
98 13 _/E 8192 unsigned module was loaded
99 14 _/L 16384 soft lockup occurred
100 15 _/K 32768 kernel has been live patched
101 16 _/X 65536 auxiliary taint, defined for
102 17 _/T 131072 kernel was built with the st
103 18 _/N 262144 an in-kernel test has been r
104 === === ====== ============================
105
106 Note: The character ``_`` is representing a bl
107 easier.
108
109 More detailed explanation for tainting
110 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
111
112 0) ``G`` if all modules loaded have a GPL or
113 any proprietary module has been loaded.
114 MODULE_LICENSE or with a MODULE_LICENSE t
115 insmod as GPL compatible are assumed to b
116
117 1) ``F`` if any module was force loaded by `
118 modules were loaded normally.
119
120 2) ``S`` if the kernel is running on a proce
121 specification: hardware has been put into
122 therefore proper execution cannot be guar
123 Kernel will be tainted if, for example:
124
125 - on x86: PAE is forced through forcepae
126 which do not report PAE but may have a
127 kernel is running on non officially cap
128 being poked at from userspace.
129 - on arm: kernel running on certain CPUs
130 having certain kernel features enabled.
131 - on arm64: there are mismatched hardware
132 bootloader has booted CPUs in different
133 - certain drivers are being used on non s
134 scsi/snic on something else than x86_64
135 x86/x86_64/itanium, have broken firmwar
136 irqchip/irq-gic on arm64 ...).
137 - x86/x86_64: Microcode late loading is d
138 tainting the kernel. It requires that a
139 the update happens when the system is a
140 a higher priority MCE/SMI/NMI can move
141 rendezvous and interrupt the update, wh
142 machine.
143
144 3) ``R`` if a module was force unloaded by `
145 modules were unloaded normally.
146
147 4) ``M`` if any processor has reported a Mac
148 ``' '`` if no Machine Check Exceptions ha
149
150 5) ``B`` If a page-release function has foun
151 unexpected page flags. This indicates a h
152 there should be other information in the
153 occurred.
154
155 6) ``U`` if a user or user application speci
156 Tainted flag be set, ``' '`` otherwise.
157
158 7) ``D`` if the kernel has died recently, i.
159
160 8) ``A`` if an ACPI table has been overridde
161
162 9) ``W`` if a warning has previously been is
163 (Though some warnings may set more specif
164
165 10) ``C`` if a staging driver has been loaded
166
167 11) ``I`` if the kernel is working around a s
168 firmware (BIOS or similar).
169
170 12) ``O`` if an externally-built ("out-of-tre
171
172 13) ``E`` if an unsigned module has been load
173 module signature.
174
175 14) ``L`` if a soft lockup has previously occ
176
177 15) ``K`` if the kernel has been live patched
178
179 16) ``X`` Auxiliary taint, defined for and us
180
181 17) ``T`` Kernel was build with the randstruc
182 produce extremely unusual kernel structur
183 pathological ones), which is important to
184 build time.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.