tar
The tar command was originally designed to be used to create backup copies of files on tape — in fact, tar actually stands for Tape ARchive. The tar command is the most common way to create a compressed archive of one or more files that you can easily move from one computer system to another.You can use the tar command to create an archive of an entire directory like this:
tar –cvf archive.tar dirname/In this example, the switch -cvf invokes three options: c, which creates a tar archive; v, which runs tar in verbose mode so that the files added to the archive are individually listed; and f, which provides the name of the archive file to be created. Next comes the name of the archive file (in this case, archive.tar). And finally comes the name of the folder that contains the files to be archived.
To extract files from an archive, use this command:
tar –xvf archive.tarHere, the -x is specified instead of -c to extract rather than create the archive. The contents of the specified archive file (in this case, archive.tar) are extracted to the current working directory.
shutdown
An easy way to shut down a Linux system from a command prompt is to issue the shutdown command. To perform an immediate shutdown, enter this command:shutdown nowTo reboot a system immediately, enter this:
shutdown -r nowTo schedule a reboot for a certain time, such as 2:00 a.m., enter this:
shutdown -r 2:00To reboot an hour from now, enter this:
shutdown –r +60
free
The free command lets you know how much free memory is available on a Linux system. Simply type the command free and you'll see output similar to the following:total used free shared buff/cache available Mem: 4030488 961888 1795920 2228 1272680 2803356 Swap: 2097148 0 2097148You can also use the -h switch to convert the numbers to KB, MB, or GB so they're easier for a human to read:
total used free shared buff/cache available Mem: 3.8G 938M 1.7G 2.2M 1.3G 2.7G Swap: 2.0G 0B 2.0GHere, you can see that the system has a total of 3.8GB of RAM, of which 938MB is used and 1.7GB is free.
df
The df command, short for disk free, lists the amount of free space available on all the disk volumes on a Linux system. For each mounted disk, df lists the total amount of disk space, the amount of space used, the amount of space that is free, and the percentage of used space.For example, enter the command df with no switches and you'll see output similar to this:
Filesystem 1K-blocks Used Available Use% Mounted on devtmpfs 2005408 0 2005408 0% /dev tmpfs 2015244 228 2015016 1% /dev/shm tmpfs 2015244 1336 2013908 1% /run tmpfs 2015244 0 2015244 0% /sys/fs/cgroup /dev/sda5 154803352 5044044 149759308 4% / tmpfs 2015244 96 2015148 1% /tmp /dev/sda2 289293 92512 177325 35% /boot tmpfs 403052 8 403044 1% /run/user/42 tmpfs 403052 24 403028 1% /run/user/1000Here, the disk space for each volume is listed in units of 1KB blocks, which translates to 2GB of disk space. Thus, the first drive (devtmpfs) has a total of 2,005,408 1KB blocks.
You can use the -h switch to get more readable results:
Filesystem Size Used Avail Use% Mounted on devtmpfs 2.0G 0 2.0G 0% /dev tmpfs 2.0G 228K 2.0G 1% /dev/shm tmpfs 2.0G 1.4M 2.0G 1% /run tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup /dev/sda5 148G 4.9G 143G 4% / tmpfs 2.0G 112K 2.0G 1% /tmp /dev/sda2 283M 91M 174M 35% /boot tmpfs 394M 8.0K 394M 1% /run/user/42 tmpfs 394M 28K 394M 1% /run/user/1000
locate
The locate command can be very helpful if you can remember some or all of a filename but you're not sure what directory the file is in. For example, suppose you need to find the directory that contains the file httpd.conf. To do so, enter this command:locate httpd.confYou'll be rewarded with the location of any file in your system with named httpd.conf. On my Linux system, there are two:
/etc/httpd/conf/httpd.conf /usr/lib/tmpfiles.d/httpd.confYou can use wildcards if you aren't sure of the exact filename. For example, to find all files with the extension .conf, use this command:
locate *.confThe result will be a listing of hundreds of files, which can be difficult to read. To limit the display to just one screen-full at a time, you can pipe the output to the more command, like this:
locate *.conf | more