Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
Check the exit status of a command
Answer:
You can check the exit status of a command by checking the special variable $?
E.g.
# ls
# echo $?
0
# foo
-bash: foo: command not found
# echo $?
127
Non zero (e.g. 127) exit status mean the command failed to execute.
Display current system hardware architecture
Answer:
arch can display the current system hardware architecture name (same as uname -m)
# arch
x86_64
How to check failed login attempt in Ubuntu
Answer:
Every login attempts are logged in the file /var/log/auth.log in Ubuntu.
To check failed login attempt(s),
E.g.
# grep 'Failed password' /var/log/auth.log
Jan 31 14:00:27 localhost sshd[16141]: Failed password...
Jan 31 14:00:46 localhost sshd[16141]: Failed password...
Jan 31 14:00:49 localhost sshd[16141]: Failed password...
How to broadcast text message to all users
Answer:
To broadcast message on the terminals of all currently logged in users, use the wall command
# echo "Hello" | wall
Execute command as another user
Answer:
If you want to run command as another user, you can use the following method:
# sudo su mark -c 'whoami'
mark
Assume currently logged in as user other than mark.
