Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
What does the run-parts mean in crontab?
Answer:
You might find the following lines in /etc/crontab
01 * * * * root run-parts /etc/cron.hourly
The actual meaning of run-parts is to run all the scripts in a given directory. So the above hourly cron means to execute all the scripts in the directory /etc/cron.hourly every hour.
See:
man run-parts
Why sometimes kill does not work
Answer:
Sometimes you might noticed that kill statement does not work in some cases, e.g.
kill program
The reason is that the kill statement send a SIGTERM signal to the target process by default and tell the process to terminate itself. However, this signal can be catch up by the process and therefore can be ignored if the program's writer choose to ignore.
To kill a process at all cost, use
kill -9 program
SIGKILL will be send instead of SIGTERM, which cannot be caught or ignored.
Prevent go way SSH session killing running job
Answer:
If you are executing a long running job over SSH session, when your SSH session is terminated for whatever reason, e.g. unstable network connection. Your long running job will die (it will receive a hangup/hup signal) when the SSH session was killed.
To overcome this, when executing long running job over SSH, use the following way
nohup program &
How to redirect output to more than one place
Answer:
It is easy to redirect output to a file by using >
E.g.
cat test.txt > foo.txt
But if you want to redirect to more than one file, you can use the tee command
E.g.
cat test.txt | tee bar.txt > foo.txt
Meaning of 2>&1 in crontab
Answer:
It is quite common to find the following line in crontab
32 5 * * * root /project/cron.sh >> /dev/null 2>&1
The meaning of 2>&1 at the end of line means to redirect the standard error stream (stderr) to the standard out stream (stdout), and finally redirect everything to /dev/null.
It is commonly used in crontab definition so if a given command return too much warnings, it will not be logged anywhere in the system in order to reduce the storage requirements.
