+++ /dev/null
-'\" t
-.\" Copyright (C) 1995 Andries Brouwer (aeb@cwi.nl)
-.\" and Copyright (C) 2012, 2014 Michael Kerrisk <mtk.manpages@gmail.com>
-.\"
-.\" %%%LICENSE_START(VERBATIM)
-.\" Permission is granted to make and distribute verbatim copies of this
-.\" manual provided the copyright notice and this permission notice are
-.\" preserved on all copies.
-.\"
-.\" Permission is granted to copy and distribute modified versions of this
-.\" manual under the conditions for verbatim copying, provided that the
-.\" entire resulting derived work is distributed under the terms of a
-.\" permission notice identical to this one.
-.\"
-.\" Since the Linux kernel and libraries are constantly changing, this
-.\" manual page may be incorrect or out-of-date. The author(s) assume no
-.\" responsibility for errors or omissions, or for damages resulting from
-.\" the use of the information contained herein. The author(s) may not
-.\" have taken the same level of care in the production of this manual,
-.\" which is licensed free of charge, as they might when working
-.\" professionally.
-.\"
-.\" Formatted or processed versions of this manual, if unaccompanied by
-.\" the source, must acknowledge the copyright and authors of this work.
-.\" %%%LICENSE_END
-.\"
-.\" Written 11 June 1995 by Andries Brouwer <aeb@cwi.nl>
-.\" 2008-02-15, Jeremy Kerr <jk@ozlabs.org>
-.\" Add info on command type 10; add details on types 6, 7, 8, & 9.
-.\" 2008-02-15, Michael Kerrisk <mtk.manpages@gmail.com>
-.\" Update LOG_BUF_LEN details; update RETURN VALUE section.
-.\"
-.TH SYSLOG 2 2014-07-08 "Linux" "Linux Programmer's Manual"
-.SH NAME
-syslog, klogctl \- read and/or clear kernel message ring buffer;
-set console_loglevel
-.SH SYNOPSIS
-.nf
-.BI "int syslog(int " type ", char *" bufp ", int " len );
-.B " /* No wrapper provided in glibc */"
-.sp
-/* The glibc interface */
-.br
-.B "#include <sys/klog.h>"
-.sp
-.BI "int klogctl(int " type ", char *" bufp ", int " len );
-.fi
-.SH DESCRIPTION
-.IR Note :
-Probably, you are looking for the C library function
-.BR syslog (),
-which talks to
-.BR syslogd (8);
-see
-.BR syslog (3)
-for details.
-
-This page describes the kernel
-.BR syslog ()
-system call, which is used to control the kernel
-.IR printk ()
-buffer; the glibc wrapper function for the system call is called
-.BR klogctl ().
-.SS The kernel log buffer
-The kernel has a cyclic buffer of length
-.B LOG_BUF_LEN
-in which messages given as arguments to the kernel function
-.BR printk ()
-are stored (regardless of their log level).
-In early kernels,
-.B LOG_BUF_LEN
-had the value 4096;
-from kernel 1.3.54, it was 8192;
-from kernel 2.1.113, it was 16384;
-since kernel 2.4.23/2.6, the value is a kernel configuration option
-.RB ( CONFIG_LOG_BUF_SHIFT ,
-default value dependent on the architecture).
-.\" Under "General setup" ==> "Kernel log buffer size"
-.\" For 2.6, precisely the option seems to have appeared in 2.5.55.
-Since Linux 2.6.6, the size can be queried with command type 10 (see below).
-.SS Commands
-The \fItype\fP argument determines the action taken by this function.
-The list below specifies the values for
-.IR type .
-The symbolic names are defined in the kernel source,
-but are not exported to user space;
-you will either need to use the numbers, or define the names yourself.
-.TP
-.BR SYSLOG_ACTION_CLOSE " (0)"
-Close the log.
-Currently a NOP.
-.TP
-.BR SYSLOG_ACTION_OPEN " (1)"
-Open the log.
-Currently a NOP.
-.TP
-.BR SYSLOG_ACTION_READ " (2)"
-Read from the log.
-The call
-waits until the kernel log buffer is nonempty, and then reads
-at most \fIlen\fP bytes into the buffer pointed to by
-.IR bufp .
-The call returns the number of bytes read.
-Bytes read from the log disappear from the log buffer:
-the information can be read only once.
-This is the function executed by the kernel when a user program reads
-.IR /proc/kmsg .
-.TP
-.BR SYSLOG_ACTION_READ_ALL " (3)"
-Read all messages remaining in the ring buffer,
-placing them in the buffer pointed to by
-.IR bufp .
-The call reads the last \fIlen\fP
-bytes from the log buffer (nondestructively),
-but will not read more than was written into the buffer since the
-last "clear ring buffer" command (see command 5 below)).
-The call returns the number of bytes read.
-.TP
-.BR SYSLOG_ACTION_READ_CLEAR " (4)"
-Read and clear all messages remaining in the ring buffer.
-The call does precisely the same as for a
-.I type
-of 3, but also executes the "clear ring buffer" command.
-.TP
-.BR SYSLOG_ACTION_CLEAR " (5)"
-The call executes just the "clear ring buffer" command.
-The
-.I bufp
-and
-.I len
-arguments are ignored.
-.IP
-This command does not really clear the ring buffer.
-Rather, it sets a kernel bookkeeping variable that
-determines the results returned by commands 3
-.RB ( SYSLOG_ACTION_READ_ALL )
-and 4
-.RB ( SYSLOG_ACTION_READ_CLEAR ).
-This command has no effect on commands 2
-.RB ( SYSLOG_ACTION_READ )
-and 9
-.RB ( SYSLOG_ACTION_SIZE_UNREAD ).
-.TP
-.BR SYSLOG_ACTION_CONSOLE_OFF " (6)"
-The command saves the current value of
-.I console_loglevel
-and then sets
-.I console_loglevel
-to
-.IR minimum_console_loglevel ,
-so that no messages are printed to the console.
-Before Linux 2.6.32,
-.\" commit 1aaad49e856ce41adc07d8ae0c8ef35fc4483245
-the command simply sets
-.I console_loglevel
-to
-.IR minimum_console_loglevel .
-See the discussion of
-.IR /proc/sys/kernel/printk ,
-below.
-
-The
-.I bufp
-and
-.I len
-arguments are ignored.
-.TP
-.BR SYSLOG_ACTION_CONSOLE_ON " (7)"
-If a previous
-.B SYSLOG_ACTION_CONSOLE_OFF
-command has been performed,
-this command restores
-.I console_loglevel
-to the value that was saved by that command.
-Before Linux 2.6.32,
-.\" commit 1aaad49e856ce41adc07d8ae0c8ef35fc4483245
-this command simply sets
-.I console_loglevel
-to
-.IR default_console_loglevel .
-See the discussion of
-.IR /proc/sys/kernel/printk ,
-below.
-
-The
-.I bufp
-and
-.I len
-arguments are ignored.
-.TP
-.BR SYSLOG_ACTION_CONSOLE_LEVEL " (8)"
-The call sets
-.I console_loglevel
-to the value given in
-.IR len ,
-which must be an integer between 1 and 8 (inclusive).
-The kernel silently enforces a minimum value of
-.IR minimum_console_loglevel
-for
-.IR len .
-See the
-.IR "log level"
-section for details.
-The
-.I bufp
-argument is ignored.
-.TP
-.BR SYSLOG_ACTION_SIZE_UNREAD " (9) (since Linux 2.4.10)"
-The call
-returns the number of bytes currently available to be read
-from the kernel log buffer via command 2
-.RB ( SYSLOG_ACTION_READ ).
-The
-.I bufp
-and
-.I len
-arguments are ignored.
-.TP
-.BR SYSLOG_ACTION_SIZE_BUFFER " (10) (since Linux 2.6.6)"
-This command returns the total size of the kernel log buffer.
-The
-.I bufp
-and
-.I len
-arguments are ignored.
-.PP
-All commands except 3 and 10 require privilege.
-In Linux kernels before 2.6.37,
-command types 3 and 10 are allowed to unprivileged processes;
-since Linux 2.6.37,
-these commands are allowed to unprivileged processes only if
-.IR /proc/sys/kernel/dmesg_restrict
-has the value 0.
-Before Linux 2.6.37, "privileged" means that the caller has the
-.BR CAP_SYS_ADMIN
-capability.
-Since Linux 2.6.37,
-"privileged" means that the caller has either the
-.BR CAP_SYS_ADMIN
-capability (now deprecated for this purpose) or the (new)
-.BR CAP_SYSLOG
-capability.
-.\"
-.\"
-.SS /proc/sys/kernel/printk
-.I /proc/sys/kernel/printk
-is a writable file containing four integer values that influence kernel
-.I printk()
-behavior when printing or logging error messages.
-The four values are:
-.TP
-.I console_loglevel
-Only messages with a log level lower than this value will
-be printed to the console.
-The default value for this field is
-.B DEFAULT_CONSOLE_LOGLEVEL
-(7), but it is set to
-4 if the kernel command line contains the word "quiet", \" since Linux 2.4
-10 if the kernel command line contains the word "debug",
-and to 15 in case
-of a kernel fault (the 10 and 15 are just silly, and equivalent to 8).
-The value of
-.IR console_loglevel
-can be set (to a value in the range 1-8) by a
-.BR syslog ()
-call with a
-.I type
-of 8.
-.TP
-.I default_message_loglevel
-This value will be used as the log level for
-.IR printk()
-messages that do not have an explicit level.
-Up to and including Linux 2.6.38,
-the hard-coded default value for this field was 4
-.RB ( KERN_WARNING );
-since Linux 2.6.39,
-.\" commit 5af5bcb8d37f99ba415a1adc6da71051b84f93a5
-the default value is a defined by the kernel configuration option
-.BR CONFIG_DEFAULT_MESSAGE_LOGLEVEL ,
-which defaults to 4.
-.TP
-.I minimum_console_loglevel
-The value in this field is the minimum value to which
-.I console_loglevel
-can be set.
-.TP
-.I default_console_loglevel
-This is the default value for
-.IR console_loglevel .
-.\"
-.\"
-.SS The log level
-Every
-.IR printk ()
-message has its own log level.
-If the log level is not explicitly specified as part of the message,
-it defaults to
-.IR default_message_loglevel .
-The conventional meaning of the log level is as follows:
-
-.TS
-lB lB lB
-lB c l.
-Kernel constant Level value Meaning
-KERN_EMERG 0 System is unusable
-KERN_ALERT 1 Action must be taken immediately
-KERN_CRIT 2 Critical conditions
-KERN_ERR 3 Error conditions
-KERN_WARNING 4 Warning conditions
-KERN_NOTICE 5 Normal but significant condition
-KERN_INFO 6 Informational
-KERN_DEBUG 7 Debug-level messages
-.TE
-
-The kernel
-.IR printk()
-routine will print a message on the
-console only if it has a log level less than the value of
-.IR console_loglevel .
-.SH RETURN VALUE
-For \fItype\fP equal to 2, 3, or 4, a successful call to
-.BR syslog ()
-returns the number
-of bytes read.
-For \fItype\fP 9,
-.BR syslog ()
-returns the number of bytes currently
-available to be read on the kernel log buffer.
-For \fItype\fP 10,
-.BR syslog ()
-returns the total size of the kernel log buffer.
-For other values of \fItype\fP, 0 is returned on success.
-
-In case of error, \-1 is returned,
-and \fIerrno\fP is set to indicate the error.
-.SH ERRORS
-.TP
-.B EINVAL
-Bad arguments (e.g.,
-bad
-.IR type ;
-or for
-.I type
-2, 3, or 4,
-.I buf
-is NULL,
-or
-.I len
-is less than zero; or for
-.I type
-8, the
-.I level
-is outside the range 1 to 8).
-.TP
-.B ENOSYS
-This
-.BR syslog ()
-system call is not available, because the kernel was compiled with the
-.BR CONFIG_PRINTK
-kernel-configuration option disabled.
-.TP
-.B EPERM
-An attempt was made to change
-.I console_loglevel
-or clear the kernel
-message ring buffer by a process without sufficient privilege
-(more precisely: without the
-.B CAP_SYS_ADMIN
-or
-.BR CAP_SYSLOG
-capability).
-.TP
-.B ERESTARTSYS
-System call was interrupted by a signal; nothing was read.
-(This can be seen only during a trace.)
-.SH CONFORMING TO
-This system call is Linux-specific and should not be used in programs
-intended to be portable.
-.SH NOTES
-From the very start, people noted that it is unfortunate that
-a system call and a library routine of the same name are entirely
-different animals.
-.\" In libc4 and libc5 the number of this call was defined by
-.\" .BR SYS_klog .
-.\" In glibc 2.0 the syscall is baptized
-.\" .BR klogctl ().
-.SH SEE ALSO
-.BR syslog (3),
-.BR capabilities (7)
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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