Linux Basic Commands

To see a list of the processes running on your machine use the ps command. Pipe it into  more

ps -ef | more

To find all the processes running under user des

ps -ef | grep des

Top will provide a real time view of processes running with some summary infomation.

top

If you find a process you would like to terminate, say PID 2056 you can use the kill command.

kill 2056

If this does not terminate the process you can force a kill with the -9 option

kill -9 2056

To find out what PID the terminal widow you are using is type in the terminal window.

echo $$

For example open a terminal  and type sleep 600 and then open another terminal and find this process using grep

sleep 600

ps -ef | grep sleep

To find a file named hostname ignoring case and searching from /

find / -iname hostname

To find all files named zulu and redirect the output into a file named zulufind ignoring errors

find / -name Zulu>zulufind 2>/dev/null

To find a file from the current directory

find . -name passwd

To ignore errors add 2>/dev/null to the end where 2 means stderror and >/dev/null redirects to a null device (basically dumps the errors to nowhere)

find / -name passwd 2>/dev/null

To make an archive we use the tar command which stands for tape archive. To make an archive of my home directory /home/des, cd to it and type

tar -cvf mytar.tar /home/des/

This will create the archive file mytar.tar in /home/des The -cvf stands for -c = create v = verbose and -f = file archive

To see a list of the contents of the tar file

tar -tvf /home/des/mytar.tar

To compress the tar file, cd  to the directory of the tar file and type

gzip  mytar.tar

This changes the tar file to a tar.gz compressed archive

To uncompress the tar.gz back to a tar

gunzip mytar.tar.gz

And to extract the archive, cd to the directory you want the files in

tar xvf  /home/des/mytar.tar

You can also use a shorcut to uncompress and unpack a tar.gz in one command

gunzip -c mytar.tar.gz | tar xopf -

You can use the short version of tar and gzip which makes a .tgz compressed archive. To archive and compress a folder named des, cd to it directory and use:

tar cvfz  des.tgz des

This creates a compressed archive named des.tgz. To extract the contents you can use:

tar xvzf des.tgz

This extracts the contents of des.tgz into the current directory.

If you want to extract into a specific directory then cd to that directory and use tar. For example if I wnat to untar into desdump directory.

mkdir desdump

cd desdump

tar xvfz ../des.tgz 

Where ../des.tgz is the relative path to the .tgz file. You could also use the full path to the file like /home/des/des.tgz

Cron is a daemon that executes scheduled commands and is started automatically from /etc/init.d when multiuser run levels are started.

To list all cron jobs

crontab -l

To start a new crontab

crontab -e

Some systems will give you a choice of editor to edit the crontab file, if you want to set yours to a specific editor permanently type

export EDITOR=vi

And to set it for nano

export EDITOR=nano

Use the same process for your favorite editor

Once the file is open add a line containing the format below followed by the command you want to run.

Minute Hour Day of month Month Day Command

0-59    0-23        1-31         1-12    0-6  

0         20           13             *        6

For example to run a cron job command looking at the amount of disk space that is free(df -h)  at 11:30 *(every day of the month) * (every month) 1-5(day of week)

30 11 * * 1-5 df -h

To run every 20 mins from 7 - 5 on mon,wed,fri

0,20,40 7-17 * * 1,3,5 du -sh /var