How to append a job to a normal user's crontab from a shell script?

nivedhitha · 08-24-2011, 04:18 AM

Hi All,

I tried to get an answer for this one, but no go. So pls post your suggestions and help me.

On an AIX system, my requirement is to build and run a script as root. This script does multiple actions. One of the tasks is to append a job to a normal users' crontab.

My basic idea is like this:
cronentry="5 * * * * /tmp/dummyscript"
crontab -u myuser -l > /tmp/cronfile
print "$cronentry >> /tmp/cronfile"

Now /tmp/cronfile contains the updated cron file. My question is, how to put this content back into myuser's cron file?.
The constraints are:
1)Other portions of the script needs root privileges. So normal user cannot execute the script.
2)It is not possible to manually edit cronfile, because this and other steps should be part of a big script that would be executed on a number of systems.
3)Root cannot give the command

Code:

crontab [file]

This would "create or replace your crontab file by copying the specified file, or standard input if file is omitted or - is specified as file , into the crontab directory, /var/spool/cron/crontabs. The name of your crontab file in the crontab directory is the same as your effective user name".

This command would modify the crontab of invoking user, which is root in my case. But I want to modify the crontab of 'myuser'.

How to modify the syntax to achieve this?.

As the remaining portions of the script are in ksh, I am not looking at the perl/expect solution.

ta0kira · 08-24-2011, 08:03 AM

Quote:

Originally Posted by nivedhitha

This command would modify the crontab of invoking user, which is root in my case. But I want to modify the crontab of 'myuser'.

You can try su - user -c 'crontab ...'.
Kevin Barry

nivedhitha · 08-25-2011, 08:51 AM

Thank you for the idea, Kevin. But the script gets stuck when I comes to the su part.

I modified it with some if conditions, to understand till what stage the script goes well.

My script is

Code:

TMPFILE=/tmp/cronfile
cronentry="5 * * * * /tmp/dummyscript"
crontab -u myuser -l >$TMPFILE

if [[ $(grep -c $cronentry $TMPFILE) != 1 ]]; then
print "cronentry not found. Adding cronentry now"
print "$cronentry" >> $TMPFILE
else
print "cronentry found"
fi
su - myuser -c 'crontab $TMPFILE'

The output is

Code:

cronentry not found. Adding cronentry now

And then it hangs here. Basically it gets stuck doing nothing.

But cat $TMPFILE does have "5 * * * * /tmp/dummyscript" in it.

Please help me correct this.

nivedhitha · 08-26-2011, 06:20 AM

Hi All,

I need help with this one. Kindly shed some light on this.

Is it hanging because su opens up a new shell?

Thanks in advance.