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SYSLOG !!!SYSLOG NAME SYNOPSIS DESCRIPTION RETURN VALUE ERRORS CONFORMING TO SEE ALSO ---- !!NAME syslog - read and/or clear kernel message ring buffer; set console_loglevel !!SYNOPSIS __#include __ ''type''__, char *__''bufp''__, int__ ''len''__); __ !!DESCRIPTION This is probably not the function you are interested in. Look at syslog(3) for the C library interface. This page only documents the bare kernel system call interface. The ''type'' argument determines the action taken by __syslog__. Quoting from ''kernel/printk.c'': /* * Commands to sys_syslog: * * 0 -- Close the log. Currently a NOP. * 1 -- Open the log. Currently a NOP. * 2 -- Read from the log. * 3 -- Read up to the last 4k of messages in the ring buffer. * 4 -- Read and clear last 4k of messages in the ring buffer * 5 -- Clear ring buffer. * 6 -- Disable printk's to console * 7 -- Enable printk's to console * 8 -- Set level of messages printed to console */ Only function 3 is allowed to non-root processes. __The kernel log buffer__ The kernel has a cyclic buffer of length LOG_BUF_LEN (4096, since 1.3.54: 8192, since 2.1.113: 16384) in which messages given as argument to the kernel function ''printk''() are stored (regardless of their loglevel). The call __syslog__ (2,''buf'',''len'') waits until this kernel log buffer is nonempty, and then reads at most ''len'' bytes into the buffer ''buf''. It returns the number of bytes read. Bytes read from the log disappear from the log buffer: the information can only be read once. This is the function executed by the kernel when a user program reads ''/proc/kmsg''. The call __syslog__ (3,''buf'',''len'') will read the last ''len'' bytes from the log buffer (nondestructively), but will not read more than was written into the buffer since the last `clear ring buffer' command (which does not clear the buffer at all). It returns the number of bytes read. The call __syslog__ (4,''buf'',''len'') does precisely the same, but also executes the `clear ring buffer' command. The call __syslog__ (5,''dummy'',''idummy'') only executes the `clear ring buffer' command. __The loglevel__ The kernel routine ''printk''() will only print a message on the console, if it has a loglevel less than the value of the variable ''console_loglevel'' (initially DEFAULT_CONSOLE_LOGLEVEL (7), but set to 10 if the kernel commandline contains the word `debug', and to 15 in case of a kernel fault - the 10 and 15 are just silly, and equivalent to 8). This variable is set (to a value in the range 1-8) by the call __syslog__ (8,''dummy'',''value''). The calls __syslog__ (''type'',''dummy'',''idummy'') with ''type'' equal to 6 or 7, set it to 1 (kernel panics only) or 7 (all except debugging messages), respectively. Every text line in a message has its own loglevel. This level is DEFAULT_MESSAGE_LOGLEVEL - 1 (6) unless the line starts with d'' is a digit in the range 1-7, in which case the level is ''d''. The conventional meaning of the loglevel is defined in '''' as follows: #define KERN_EMERG !!RETURN VALUE In case of error, -1 is returned, and ''errno'' is set. Otherwise, for ''type'' equal to 2, 3 or 4, __syslog__() returns the number of bytes read, and otherwise 0. !!ERRORS __EPERM__ An attempt was made to change console_loglevel or clear the kernel message ring buffer by a process without root permissions. __EINVAL__ Bad parameters. __ERESTARTSYS__ System call was interrupted by a signal - nothing was read. !!CONFORMING TO This system call is Linux specific and should not be used in programs intended to be portable. !!SEE ALSO syslog(3) ----
6 pages link to
syslog(2)
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Man2s
sysklogd(8)
syscalls(2)
syslog.conf(5)
proc(5)
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