= Basis =
==Calling syslog method from shell==
To do that, use '''logger''' command :
<pre class="target">
# logger -t "MYTAGNAME" "I like otters with cream"
</pre>

You can then see the message in /var/log/messages:
<pre class="target">
# tail /var/log/messages
...
Oct 16 16:50:13 armadeus user.notice MYTAGNAME: I like otters with cream
</pre>

==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 :
<source lang="C">
...
#include <syslog.h>

int main(int argc, char *argv[])
{
...
openlog("program_name", LOG_PID, LOG_USER);
...
closelog();
...
}
</source>
Then, you can call syslog from your code using printf like format :
<source lang="C">
...
syslog(LOG_INFO, "%s called with %d arguments\n", argv[0], argc);
...
</source>
If you compile the source file:
<source lang="C">
// 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;
}
</source>
With the command :
<pre class="apf">
itsme@mycomputer:~/log_syslog$ gcc log_syslog.c -o log-syslog
</pre>
Then run it 2 times :
<pre class="apf">
itsme@mycomputer:~/log_syslog$ ./log_syslog
itsme@mycomputer:~/log_syslog$ ./log_syslog pim pam poum
</pre>
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)
<pre class="apf">
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
</pre>
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 :

<pre class="host">
$ make busybox-menuconfig
</pre>

The configuration menu can be found here :

<pre class="config">
System Logging Utilities --->
</pre>

== Buildroot packages ==

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

<pre class="host">
$ make menuconfig
</pre>

Select option :
<pre class="config">
Package Selection for the target --->
[*] Show packages that are also provided by busybox
</pre>

Then go to following menu and choose your prefered syslog implementation ;-):
<pre class="config">
Target packages --->
System tools --->
...
[ ] rsyslog
...
[ ] sysklogd
...
[ ] syslog-ng
...
</pre>

== 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:
<source lang="bash">
# 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
</source>

UsingSyslog

2025-10-10T12:50:43Z

JulienB:

= Basis =
==Calling syslog method from shell==
To do that, use '''logger''' command :
<pre class="target">
# logger -t "MYTAGNAME" "I like otters with cream"
</pre>

You can then see the message in /var/log/messages:
<pre class="target">
# tail /var/log/messages
...
Oct 16 16:50:13 armadeus user.notice MYTAGNAME: I like otters with cream
</pre>

==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 :
<source lang="C">
...
#include <syslog.h>

int main(int argc, char *argv[])
{
...
openlog("program_name", LOG_PID, LOG_USER);
...
closelog();
...
}
</source>
Then, you can call syslog from your code using printf like format :
<source lang="C">
...
syslog(LOG_INFO, "%s called with %d arguments\n", argv[0], argc);
...
</source>
If you compile the source file:
<source lang="C">
// 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;
}
</source>
With the command :
<pre class="apf">
itsme@mycomputer:~/log_syslog$ gcc log_syslog.c -o log-syslog
</pre>
Then run it 2 times :
<pre class="apf">
itsme@mycomputer:~/log_syslog$ ./log_syslog
itsme@mycomputer:~/log_syslog$ ./log_syslog pim pam poum
</pre>
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)
<pre class="apf">
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
</pre>
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 :

<pre class="host">
$ make busybox-menuconfig
</pre>

The configuration menu can be found here :

<pre class="config">
System Logging Utilities --->
</pre>

== Buildroot packages ==

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

<pre class="host">
$ make menuconfig
</pre>

Select option :
<pre class="config">
Package Selection for the target --->
[*] Show packages that are also provided by busybox
</pre>

Then go to following menu and choose your prefered syslog implementation ;-):
<pre class="config">
Target packages --->
System tools --->
...
[ ] rsyslog
...
[ ] sysklogd
...
[ ] syslog-ng
...
</pre>

== 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:
<code source="bash">
# 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
</code>

2025-02-20T16:53:54Z

JulienB:

preempt-rt are a series of patches to improve Linux kernel realtime performances. This page explain how to use it.

==Installation==
* Depending on your board, you may have a Buildroot defconfig to apply preempt-rt patches automagically. For example for [[OPOS6UL]]:
<pre class=host>
$ make opos6ul-preempt-rt_defconfig
</pre>

* If no config is available, you will have to do the job yourself, by finding a kernel version compatible with preempt-rt patches from https://www.kernel.org/pub/linux/kernel/projects/rt/

==Usage==
* You can change realtime priority of tasks with ''chrt''. For example to set process X to priority 20 in FIFO scheduling queue, you have to do:
<pre class=apf>
# chrt -p -f 20 X

pid X's current scheduling policy: SCHED_OTHER
pid X's current scheduling priority: 0
pid X's new scheduling policy: SCHED_FIFO
pid X's new scheduling priority: 20
</pre>
* The more priority you set, the more your process is prioritary.
* Priority queues are OTHER (no realtime), FIFO (First In First Out), RR (Round Robin time share)
* You can validate realtime performances of your system with ''cyclictest''. For example to launch 10 processes triggering on timer set to 10ms with different descending priorities, you can do:
<pre class=apf>
# cyclictest -t 10 -p 20 -n -i 10000 --priospread

/dev/cpu_dma_latency set to 0us
policy: fifo: loadavg: 0.45 0.23 0.10 1/86 230

T: 0 ( 219) P:99 I:10000 C: 34012 Min: 67 Act: 166 Avg: 174 Max: 536
T: 1 ( 220) P:98 I:10500 C: 32393 Min: 76 Act: 228 Avg: 202 Max: 719
T: 2 ( 221) P:97 I:11000 C: 30920 Min: 66 Act: 170 Avg: 197 Max: 1154
T: 3 ( 222) P:96 I:11500 C: 29576 Min: 65 Act: 217 Avg: 194 Max: 1176
T: 4 ( 223) P:95 I:12000 C: 28343 Min: 72 Act: 167 Avg: 194 Max: 1912
...
</pre>
* times are in microseconds

==Links==
* https://wiki.linuxfoundation.org/realtime/documentation/howto/applications/preemptrt_setup
* https://wiki.linuxfoundation.org/realtime/documentation/howto/applications/application_base

[[Category:Real-Time]]