System & Shell commands

Posted on February 28, 2010 by Kev

Run a process detached to the current terminal:
```
nohup my_command &
```
Get the exit code of the latest runned command:
```
echo $?
```
Run the last command as root (source):
```
sudo !!
```
Show the user under which I’m currently logged in:
```
whoami
```
List cron jobs of the current user:
```
crontab -l
```

If you have the following error:

-bash: ./myscript.sh: /bin/bash^M: bad interpreter: No such file or directory

Then the fix consist of removing the bad characters:

sed -i 's/\r//' ./myscript.sh

Free up some memory by clearing RAM caches (source):
```
sync ; echo 3 > /proc/sys/vm/drop_caches
```
Display which distro is running the system (source):
```
lsb_release -a
```
or
```
cat /etc/lsb-release
```

List of most used commands:

history | awk '{a[$2]++}END{for(i in a){print a[i] " " i}}' | sort -rn | head

Disable a service on Debian/Ubuntu, then re-enable it:

update-rc.d my-service-name remove
update-rc.d my-service-name defaults

Same thing as above but on a RedHat-like system:
```
chkconfig sshd --del
chkconfig sshd --add
```

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3 thoughts on “System & Shell commands”

djib on February 28, 2010 at 17:17 said:

Another tip: if you have screen and retty on your computer, you can move an application to a screen by using screen retty $PID. I like it better than nohup because you can keep the interactivity with the process.
kev on March 1, 2010 at 15:24 said:

@djib: you’re absolutely right ! screen is a really good tool. To be honest playing with it is on my TODO list for what… 5 years ? It’s just that because I know nohup exists I don’t have any strong incensitive to learn screen…
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