Confusion with "su -c" and quotes, user context switching?


 
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Top Forums Shell Programming and Scripting Confusion with "su -c" and quotes, user context switching?
# 1  
Old 05-28-2013
Confusion with "su -c" and quotes, user context switching?

Trying to execute commands for different Unix user with that user's environment variable context without fully switching as that user using sudo && su capabilities.
Hoping this would help with security and not having to waste time switching between 10 different app users on same server.

I do not understand why 'ls' command would not get executed, but 'ls -l' would from below output!?..
Does anyone know why?

( Using solaris8, ksh Version: M-11/16/88 )
Code:
 
/home/userA>sudo -l
(root) /usr/bin/su - userB *
 
/home/userA>sudo /usr/bin/su - userB '/bin/ls' 
ksh: ls: cannot execute
 
# double quotes do not make any difference
/home/userA>sudo /usr/bin/su - userB "/bin/ls"
ksh: /bin/ls: cannot execute
 
 # Here " -c " option makes this work !
/home/userA>sudo /usr/bin/su - userB -c '/bin/ls'
folderA folderB fileA fileB ...
 
# giving command options make this work.. why?
/home/userA>sudo /usr/bin/su - userA '/bin/ls -l' 
drwxr-x--x 8 userB groupX 8192 Jan 1 00:20 BKUP
..........

Please explain what difference does "-c" really make?
I am able to execute commands as a sudo userB and his env variables(.profile, .login etc) without "-c" option as well.

[QUOTE]
/home/userA> man su
.........
Example 2: Becoming User bin and Changing to bin's Login
Environment
To become user bin but change the environment to what would
be expected if bin had originally logged in, execute:
example% su - bin
Example 3: Executing command with user bin's Environment and
Permissions
To execute command with the temporary environment and per-
missions of user bin, type:
example% su - bin -c "command args"
[/QUOTE]

Last edited by kchinnam; 05-28-2013 at 09:02 PM.. Reason: formatting
# 2  
Old 05-28-2013
This is how I do it:

Code:
 
su -c 'command-to-be-run-under-new-user' new-user

# 3  
Old 05-28-2013
I just tried your way of doing it,, it seems even worse, at least on my server..
Code:
 
/home/userA>sudo /usr/bin/su -c '/bin/ls -l' userB
Sorry, user userA is not allowed to execute '/usr/bin/su -c /bin/ls -l userB' as root on serverX.

Most of the commands I tested so far are working fine with either --> su - <userid> '<command>' or su -c <userid> '<command>'.

My problem is why a simple command like 'ls' would not work but 'ls -l' does, making this a scary half baked solution..
# 4  
Old 05-28-2013
Quote:
Originally Posted by kchinnam
Code:
  
/home/userA>sudo /usr/bin/su - userB '/bin/ls' 
ksh: ls: cannot execute

That's asking ksh to interpret ls, which it cannot do because /bin/ls is not a ksh script; it's a binary executable.

Compare
Code:
ksh /bin/ls

versus
Code:
ksh -c /bin/ls

Regards,
Alister
This User Gave Thanks to alister For This Post:
# 5  
Old 05-29-2013
Got it.
ksh man page is more clear about what ' -c ' does ---->
Code:
 -c command-string the shell executes the command(s) contained in command-string

If I put a space character after 'ls', its working, does space tell shell that its not a script, but its a command !?
Code:
 
/home/userA>ksh 'ls'    
ksh: ls: cannot execute
/home/userA>ksh 'ls '
folderA folderB fileA fileB ...


Last edited by kchinnam; 05-29-2013 at 12:46 AM.. Reason: updated statements
# 6  
Old 05-30-2013
This is indeed an undocumented(?) feature of ksh,
and is also implemented in pdksh. (But not implemented in sh,bash,zsh.)
Code:
ksh "command args"

behaves like
Code:
ksh -c "command args"

and it is sufficient to provide a space without args
Code:
ksh "command "

But better use the explicit -c because it works with all shells!
These 2 Users Gave Thanks to MadeInGermany For This Post:
# 7  
Old 06-03-2013
Appreciate you taking time to clarify this.. I will make a note of it and use 'su -c'.

Last edited by kchinnam; 06-03-2013 at 08:19 AM.. Reason: grammar
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