limit Unix command to user

                                                                     
                                             
we want to limit the activities or command to run for specific user then, how to limit a shell? here are the steps to create limited shell.

Add a user who can execute some specific commands.

1. Create a link named ‘rbash’ from bash.

# ln -s /bin/bash /opt/rbash

2. Add a user that his default shell is rbash and set he can execute only ‘ping’.

# useradd lsuser -s /opt/rbash
# passwd lsuser
# mkdir /home/lsuser/bin
# ln -s /bin/ping /home/lsuser/bin/ping
# chown root. /home/lsuser/.bash_profile
# chmod 755 /home/lsuser/.bash_profile
# vi /home/lsuser/.bash_profile

  # change PATH like follows
  PATH= $HOME/bin

3. Login with the test user.

$ cd
-rbash: cd: restricted # denied
$ ls
-rbash: ls: command not found # none
$ ping localhost
PING localhost (127.0.0.1) 56(84) bytes of data.
64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.045 ms
64 bytes from localhost (127.0.0.1): icmp_seq=2 ttl=64 time=0.008 ms
64 bytes from localhost (127.0.0.1): icmp_seq=3 ttl=64 time=0.008 ms

— localhost ping statistics —
3 packets transmitted, 3 received, 0% packet loss, time 2157ms
rtt min/avg/max/mdev = 0.008/0.020/0.045/0.017 ms　 # executed