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
Run all scripts under in a directory
Answer:
Create the following bash script, and execute it
for FILE in /project/scripts/*.sh
do
if [-f $FILE -a -x $FILE]
then
$FILE
fi
done
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 combine insert & update in a single SQL statement
Answer:
It is quite common to check if a given record already exist in database (check by primary key), insert it if not found, or update it if found.
It can be easily done using the MySQL's ON DUPLICATE KEY UPDATE statement
INSERT INTO `foo` (id, num) values (1, 0)
ON DUPLICATE KEY UPDATE num = num + 1;
Reference: http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html
