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proc.5: Document /proc/sys/kernel/sysctl_writes_strict 

Based on text in Documentation/sysctl/kernel.txt.

Cowritten-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2015-05-08 16:52:55 +02:00
parent ba5ed753c5
commit 62184395b3
1 changed files with 50 additions and 0 deletions
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@ -4151,6 +4151,56 @@ This file
specifies the system-wide maximum number of System V shared memory
segments that can be created.
.TP
.IR /proc/sys/kernel/sysctl_writes_strict " (since Linux 3.16)"
.\" commit f88083005ab319abba5d0b2e4e997558245493c8
.\" commit 2ca9bb456ada8bcbdc8f77f8fc78207653bbaa92
.\" commit f4aacea2f5d1a5f7e3154e967d70cf3f711bcd61
.\" commit 24fe831c17ab8149413874f2fd4e5c8a41fcd294
The value in this file determines how the file offset affects
the behavior of updating entries in files under
.IR /proc/sys .
The file has three possible values:
.RS
.TP 4
\-1
This provides legacy handling, with no printk warnings.
Each
.BR write (2)
must fully contain the value to be written,
and multiple writes on the same file descriptor
will overwrite the entire value, regardless of the file position.
.TP
0
(default) This provides the same behavior as for \-1,
but printk warnings are written for processes that
perform writes when the file offset is not 0.
.TP
1
Respect the file offset when writing strings into
.I /proc/sys
files.
Multiple writes will
.I append
to the value buffer.
Anything written beyond the maximum length
of the value buffer will be ignored.
Writes to numeric
.I /proc/sys
entries must always be at file offset 0 and the value must be
fully contained in the buffer provided to
.BR write (2).
.\" FIXME .
.\" With /proc/sys/kernel/sysctl_writes_strict==1, writes at an
.\" offset other than 0 do not generate an error. Instead, the
.\" write() succeeds, but the file is left unmodified.
.\" This is surprising. The behavior may change in the future.
.\" See thread.gmane.org/gmane.linux.man/9197
.\" From: Michael Kerrisk (man-pages <mtk.manpages@...>
.\" Subject: sysctl_writes_strict documentation + an oddity?
.\" Newsgroups: gmane.linux.man, gmane.linux.kernel
.\" Date: 2015-05-09 08:54:11 GMT
.RE
.TP
.I /proc/sys/kernel/sysrq
This file controls the functions allowed to be invoked by the SysRq key.
By default,