Tip#9 Some OS utilities (Unix)

NOHUP :

nohup (no hangups) is a UNIX command that allows you to execute a command in the background while you are logged into UNIX. The background process will continue to run until completion, even if you log off. For long running processes, this is a nice way to execute them. In my case, it allows me to log into a client server remotely, execute a process interactively with nohup, and then disconnect. Another benefit of nohup is that by default, a log of all activity is recorded in the current directory in the file nohup.out . e.g.

nohup sqlplus user/pwd @sqlscript &

Note : & at the end is for running the process in the background

SKILL:

Sometime I have a situations where I find that a process is consuming a lot of CPU and memory, but I don't want to kill it and I just wished if I could just 'pause' the process and that's where SKILL really helps me. e.g Process ID 1234 is taking too much resources and I need to somehow get other 'important' things done I will execute following command,

skill -STOP 1234

Once I have finished other 'important' things done I can free the process with following command

skill -CONT 1234

The nice feature is you can pass not just PID but also User, Terminal ID OR Command which makes it more powerful then I initially thought. e.g. You can 'pause' all RMAN commands on DB server with

skill -STOP rman

SNICE:

The command snice is similar to skill but Instead of stopping a process it makes its priority a lower one. e.g. for the same heavy process 1234 I could decrease the priority by using something like this,

snice +4 -p 1234

Note: +4 means we are increasing the Nice Value and effectively the higher the number, the lower the priority.

This utility is quite useful in reducing priorities.