path: root/Documentation/kernel-parameters.txt
diff options
authorBorislav Petkov <bp@suse.de>2016-08-02 14:04:07 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-08-02 19:35:06 -0400
commit750afe7babd117daabebf4855da18e4418ea845e (patch)
tree21aaf3748d3afd3e880b6ef301128c5567a15956 /Documentation/kernel-parameters.txt
parent6b1d174b0c27b5de421eda55c2731f32b6bd9852 (diff)
printk: add kernel parameter to control writes to /dev/kmsg
Add a "printk.devkmsg" kernel command line parameter which controls how userspace writes into /dev/kmsg. It has three options: * ratelimit - ratelimit logging from userspace. * on - unlimited logging from userspace * off - logging from userspace gets ignored The default setting is to ratelimit the messages written to it. This changes the kernel default setting of "on" to "ratelimit" and we do that because we want to keep userspace spamming /dev/kmsg to sane levels. This is especially moot when a small kernel log buffer wraps around and messages get lost. So the ratelimiting setting should be a sane setting where kernel messages should have a bit higher chance of survival from all the spamming. It additionally does not limit logging to /dev/kmsg while the system is booting if we haven't disabled it on the command line. Furthermore, we can control the logging from a lower priority sysctl interface - kernel.printk_devkmsg. That interface will succeed only if printk.devkmsg *hasn't* been supplied on the command line. If it has, then printk.devkmsg is a one-time setting which remains for the duration of the system lifetime. This "locking" of the setting is to prevent userspace from changing the logging on us through sysctl(2). This patch is based on previous patches from Linus and Steven. [bp@suse.de: fixes] Link: http://lkml.kernel.org/r/20160719072344.GC25563@nazgul.tnic Link: http://lkml.kernel.org/r/20160716061745.15795-3-bp@alien8.de Signed-off-by: Borislav Petkov <bp@suse.de> Cc: Dave Young <dyoung@redhat.com> Cc: Franck Bui <fbui@suse.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/kernel-parameters.txt')
1 files changed, 7 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index e24aa11e8f8a..b240540e49f2 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3173,6 +3173,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
Format: <bool> (1/Y/y=enable, 0/N/n=disable)
default: disabled
+ printk.devkmsg={on,off,ratelimit}
+ Control writing to /dev/kmsg.
+ on - unlimited logging to /dev/kmsg from userspace
+ off - logging to /dev/kmsg disabled
+ ratelimit - ratelimit the logging
+ Default: ratelimit
printk.time= Show timing data prefixed to each printk message line
Format: <bool> (1/Y/y=enable, 0/N/n=disable)