what does this command mean "sudo su - -s /bin/bash jenkins"

I couldn't understand what this command does "sudo su - -s /bin/bash jenkins". Is it log in as jenkins user under the current shell?



root@monitor:/home/jyu$ su - jenkins
su: user - does not exist
root@monitor:/home/jyu$ cat /etc/passwd | grep jenkins
root@monitor:/home/jyu$ sudo su - -s /bin/bash jenkins
Last login: Fri Jul 15 17:17:09 UTC 2016 on pts/1
[jenkins@monitor ~]$ whoami
jenkins
[jenkins@monitor ~]$ ls -alth
total 56K
-rw------- 1 jenkins jenkins 8.5K Jul 15 17:44 .bash_history
drwx------ 2 jenkins jenkins 4.0K Jul 15 16:55 .ssh
drwxr-xr-x 4 jenkins jenkins 4.0K Jul 15 16:55 .
-rw------- 1 jenkins jenkins  11K Jul 15 16:55 .viminfo
drwxr-xr-x 8 root    root    4.0K May 27 22:26 ..
drwxr-xr-x 3 jenkins jenkins 4.0K Jul  8  2014 .java
-rw-r--r-- 1 jenkins jenkins   18 Jul  3  2014 .bash_logout
-rw-r--r-- 1 jenkins jenkins  124 Jul  3  2014 .bashrc
-rw-r--r-- 1 jenkins jenkins  171 Jul  3  2014 .kshrc
-rw-r--r-- 1 jenkins jenkins  176 Jul  3  2014 .bash_profile
[jenkins@monitor ~]$
Jason YuAsked:
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woolmilkporcConnect With a Mentor Commented:
You're using "sudo" to run the command "su" (substitute user) as root, with the parameters
"-" (start a login shell),
"-s /bin/bash" (use /bin/bash instead of the default shell)
"jenkins" (substitute user jenkins).

So yes, basically you're logging in as jenkins, starting bash as a login shell.

I assume that "su - jenkins" doesn't work saying "user - does not exist" because in your environment "su" is already an alias for "su -".

Run "alias su" to verify"

"su" works after "sudo" because sudo doesn't observe alias settings.
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Jason YuAuthor Commented:
Yes, you are right. In my environment, su is an alias of "su -".

root@monitor:/home/jyu$ alias su
alias su='su -'
root@monitor:/home/jyu$
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woolmilkporcCommented:
That's why "su - jenkins" throws an error.
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