some useful tricks for linux

If you want to know more about your Linux system. Where can you get detailed information?

The best way to obtain information about your Linux system is by running the ‘uname’ command with various options. Here are the details of the available options…

Execute ‘uname’ without any options to display the kernel name:

# uname -s
Linux

Execute ‘uname’ with the -r option to display the kernel release…

# uname -r
3.8.0-23-generic

Execute ‘uname’ with the -v option to display the kernel version:

# uname -v
#34-Ubuntu SMP Wed May 29 20:22:58 UTC 2013

Execute ‘uname’ with the -m option to display the machine hardware:

# uname -m
x86_64

Execute ‘uname’ with the -o option to display the operating system:

# uname -o
GNU/Linux

What if you want to read only the first or last few lines of a file?

You can use ‘head’ and ‘tail’ commands for this.

# tail -5 output
/etc/brltty/en-nabcc.ttb
/etc/brltty/brl-al-abt_small.ktb
/etc/brltty/brl-al-abt_basic.kti
/etc/acpi/mediabtn.sh
/etc/fstab.d

The ‘tail’ command above displays the last five lines from the file ‘output’.

Through this command, you can also display the last ‘n’ bytes using the -c option:

#tail -c10 output
c/fstab.d

So, you can see that last 10 bytes were displayed in the output.

Similarly, there is a ‘head’ command to display content from the beginning of a file. Here are some examples:

#head -10 output
/boot/abi-3.8.0-19-generic
/boot/abi-3.8.0-23-generic
/boot/grub/i386-pc/search_label.mod
/sbin/acpi_available
/sbin/ip6tables
/sbin/e2label
/sbin/ntfslabel
/sbin/swaplabel
/sbin/iptables-save
/sbin/ip6tables-restore

#head -c10 output
/boot/abi-

Running a command from your history:

Sometimes you know that you ran a command a while ago and you want to run it again. You know a bit of the command, but you don’t exactly know all options, or when you executed the command.

                               Of course, you could just keep pressing the Up Arrow until you encounter the command again, but there is a better way.

You can search the bash history in an interactive mode by pressing Ctrl + r. This will put bash in history mode, allowing you to type a part of the command you’re looking for. In the meanwhile, it will show the most recent occasion where the string you’re typing was used. If it is showing you a too recent command, you can go further back in history by pressing Ctrl + r again and again. Once you found the command you were looking for, press enter to run it. If you can’t find what you’re looking for and you want to try it again or if you want to get out of history mode for an other reason, just press Ctrl + c. By the way, Ctrl + c can be used in many other cases to cancel the current operation and/or start with a fresh new line.