Does a su carry through to a script called by another script

anon091 · 10-21-2013, 02:57 PM

Say I have a cron'd script in root's crontab like this

1 1 * * * su - MyUser -c "/script/MyScript.sh"

and in MyScript.sh it runs AnotherScript.sh.

So MyUser will run in MyUser's environment/shell, but by default does that also mean AnotherScript.sh will too? or will that then run in root's?

rtmistler · 10-21-2013, 03:05 PM

My interpretation is that the second script, since it is invoked from within the first script, will inherit the user and environment from the first script.

To validate this, you can always echo out to a log file the user and environment information relevant to this and settle the issue.

anon091 · 10-21-2013, 03:07 PM

Thanks. That's how I took it too, but I guess I'll find out.

How would I echo that stuff out? I'm just trying to tweak some existing scripts I inherited.

rtmistler · 10-21-2013, 03:22 PM

Determine environment variables you wish to see and put in lines like this. Note if you use single >, you will create a new file, double >> appends, but will create if no file exists. Be careful in that it will place the file in the directory the script is running in. I usually use an explicit path when I do this.

Code:

echo $PATH >> /home/users/myuser/logs/logfile.txt
echo $USERNAME >> /home/users/myuser/logs/logfile.txt

In a login shell, type "env" and you'll see a dump of your environment and all the variable names so you can pick the ones that will be useful to you. PWD is also a good one.

Another good shell thing to do is to check returns from commands. For instance if you perform a copy, or move, or tar, something like that, you can check the return from that command:

Code:

cp file-a.txt file-b.txt;
echo $?

A ZERO indicates the copy worked. A non-ZERO indicates a fault. The "$?" is the shell variable for the default return from the last call.

anon091 · 10-21-2013, 03:26 PM

Very cool, I will have to give this stuff a try, thanks!

Firerat · 10-21-2013, 03:55 PM

why not just setup the MyUser's crontab?

Code:

su MyUser -c "crontab -e"

Code:

1 1 * * * /script/MyScript.sh

anon091 · 10-21-2013, 03:57 PM

When the AnotherScript.sh runs it doesn't work right when running in cron's env/shell, but it runs right if I run it like that, so i'm hoping if I run MyScript like that which runs AnotherScript, it will run properly.

Firerat · 10-21-2013, 04:00 PM

Quote:

Originally Posted by rjo98

When the AnotherScript.sh runs it doesn't work right when running in cron's env/shell, but it runs right if I run it like that, so i'm hoping if I run MyScript like that which runs AnotherScript, it will run properly.

then setup cron's env correctly

Code:

man 5 crontab

TobiSGD · 10-21-2013, 04:01 PM

Quote:

Originally Posted by rjo98

su - MyUser -c "/script/MyScript.sh"

This is not a valid su command. From the su manpage:

Code:

 -, -l, --login
           Provide an environment similar to what the user would expect had the user logged in directly.

           When - is used, it must be specified as the last su option. The other forms (-l and --login) do not have this restriction.

So I would recommend to change it to one of these:

Code:

su -l MyUser -c "/script/MyScript.sh"
su --login MyUser -c "/script/MyScript.sh"
su MyUser -c "/script/MyScript.sh" -