UsingSyslog

Basis

Calling syslog method from shell

To do that, use logger command :

# logger -t "MYTAGNAME" "I like otters with cream"

You can then see the message in /var/log/messages:

# tail /var/log/messages 
...
Oct 16 16:50:13 armadeus user.notice MYTAGNAME: I like otters with cream

Calling syslog method from your C source code

This part is quite simple, but we need to correctly use each parameter. First step is to declare us as syslog client :

...
#include <syslog.h>

int main(int argc, char *argv[])
{
    ...
    openlog("program_name", LOG_PID, LOG_USER);
    ...
    closelog();
    ...
}

Then, you can call syslog from your code using printf like format :

    ...
    syslog(LOG_INFO, "%s called with %d arguments\n", argv[0], argc);
    ...

If you compile the source file:

// log_syslog.c
#include <syslog.h>

int main(int argc, char *argv[])
{
    openlog("program_name", LOG_PID, LOG_USER);
    syslog(LOG_INFO, "%s called with %d arguments", argv[0], argc - 1);
    closelog();
    return 0;
}

With the command :

itsme@mycomputer:~/log_syslog$ gcc log_syslog.c -o log-syslog

Then run it 2 times :

itsme@mycomputer:~/log_syslog$ ./log_syslog
itsme@mycomputer:~/log_syslog$ ./log_syslog pim pam poum

You will probably obtain no result in shell, but you can take a look in your system log (/var/log/syslog or /var/log/messages)

itsme@mycomputer:~/log_syslog$ tail -n 2 /var/log/syslog
Sep 19 18:46:49 mycomputer program_name[3022]: ./log_syslog called with 0 arguments
Sep 19 18:46:53 mycomputer program_name[3023]: ./log_syslog called with 3 arguments

We can notice, that the lines contain program_name[PID] pattern showing us the name we have specified in openlog and the pid of the process because we ask it with LOG_PID argument.

Packages

Busybox

By default, syslog is managed by busybox, it can be configured using menuconfig :

$ make busybox-menuconfig

The configuration menu can be found here :

System Logging Utilities  --->

Buildroot packages

Some other packages are available under buildroot. To see it launch buildroot menuconfig :

$ make menuconfig

Select option :

Package Selection for the target  --->
    [*]   Show packages that are also provided by busybox

Then go to following menu and choose your prefered syslog implementation ;-):

Target packages  --->
    System tools  --->
        ...
        [ ] rsyslog
        ...
        [ ] sysklogd
        ...
        [ ] syslog-ng
        ...

Tips

• By default logs are not persistent (/var/log points to /tmp). To have persistent logs with rotation every 1Mbytes, one can try to add this to his post_build.sh script:

# for persistent and rotating log messages
rm -rf $1/var/log
mkdir $1/var/log
sed -i -e 's/SYSLOGD_ARGS=""/SYSLOGD_ARGS="-s 1024 -b 10"/' $1/etc/init.d/S01syslogd