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Switching user inside a shell script

 
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# 1  
Old 12-06-2009
Switching user inside a shell script
Dear All,

I want to switch a user inside a shell script.My current user say x and user y to whom i want to switch both have login on the same server,the one on which i want to execute my script on.
"I want to do something like this
su - y
Password should be provided in the script itself.And then i want execute a simple command as user y and then switch back to user x.Please help me as i am stuck in middle of something.

Please note iam not the root user.



Thanks
Navjot
# 2  
Old 12-06-2009
If you want to run something as another user you either have to have SUDO set up to allow this (by root) or the owner of the other "program" should set the SUID bit.

On many (or maybe all?) systems SUID has no effect with shell scripts.

Code:
$ ls -l Test*
-r-sr-xr-x  1 user2  staff  8800 Dec  6 13:46 TestCProg # C Program
-r-sr-xr-x  1 user2  staff    35 Dec  6 13:19 TestScript # Shell script

$ id user2
uid=502(user2) gid=20(staff)

$ ./TestCProg > /dev/null &; ps -ef | grep TestCProg
[1]	97055
  502 97055 96971   0   0:00.00 ttys000    0:00.00 ./TestCProg
  501 97057 96971   0   0:00.00 ttys000    0:00.00 grep TestCProg

$ ./TestScript &; ps -ef | grep TestScript
[2]	97063
  501 97063 96971   0   0:00.00 ttys000    0:00.00 ./TestScript
  501 97065 96971   0   0:00.00 ttys000    0:00.00 grep TestScript

Another option is to use the Expect tool. This is the first time I've used it, so probably not very good, but...

Code:
/usr/bin/expect << !
spawn su - y
expect "Password:"
send "y_password\r"
send "who am i\r"
send "exit\r"
expect "exit"
!

$ who am i
x        ttys000  Dec  6 15:49
$ ./Test
spawn su - y
Password:
y$ who am i
y        ttys002  Dec  6 15:50 
y$ exit

It should also be possible to use SSH to do what you want, but you'd need to set up the keys the first time
# 3  
Old 12-07-2009
Hi scott,

Although the idea is great.But ,its not a very secured one.Is there any way through which i could pass the password through a file and then login and execute the command through other user and finally get back to the original user.
# 4  
Old 12-07-2009
Hi.

With su? No, I don't think so.

And what you are suggesting is no more secure than what I suggested. Storing passwords in text files in plain text can never be considered "secure"!
# 5  
Old 12-07-2009
Hi scott,
let me explain u it a little more clearly:-

Im working on same server with two ids say x and y:-

IM not the root:-
What i want to do is
1.login through x
2.then login through y'
3.exec `command x through user y > file on user x directory`
4.exit y

I cant change the permissions of the command/script that i will have to exec as user y.
# 6  
Old 12-07-2009
I understood what you were asking.

But you can't use su - y without being prompted for a password. (unless someone else here can show how - I certainly couldn't figure it out).

You can use RSH for this, but user "y" has to set up the .rhosts file. And, and I said, SUDO and SSH are other options.

If you want a password-less login, these are your options. Otherwise you have to enter a password manually.
# 7  
Old 12-07-2009
You could try this expect script:
however your password will be stored in plain text. if you have permission you can chmod it to 500 and only you(and roots) can read it, but your password will be in plain text still.
I haven't tested this code yet either.

Code:
#!/usr/bin/expect -f

log_file /tmp/status.log

set timeout 2

spawn su - y
 log_user 0
   expect "assword: "
   send "password\r"
   expect "*> "
 log_user 1
   send "commandme\r"
   expect "*> "
   send "exit\r"

 
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