7 Extremely Useful Linux Commands for Beginners

#1: ls : What’s in this directory?

The command ls stands for list directory contents. And, cleverly, it will do just that: list a directory’s contents! Using it with -F will give a list of the directories contents, and denote items that are other directories with a trailing /.

ls -F

On my server returns:

allthethings.txt important.doc Indominus/ Misc/ probs.xls Red Wings/ Spreadsheets/ Work/

In the above case, allthethings.txt, garbage.file, important.doc, and probs.xls are files, and Indominus, Misc, Red Wings, Spreadsheets, and Work, each with the trailing /, are directories!

There are many other options, or switches, such as -F that can be used with ls for improved results. For example:

ls -lFa

Returns:

dr-xr-x---. 10 root root 4096 Apr 17 12:01 .
drwxr-xr-x. 19 root root 4096 Apr 14 12:45 ..
-rw-r--r-- 1 root root 0 Apr 17 12:00 allthethings.txt
-rw------- 1 root root 483 Apr 14 12:45 .bash_history
-rw-r--r--. 1 root root 18 Dec 28 2013 .bash_logout
-rw-r--r--. 1 root root 176 Dec 28 2013 .bash_profile
-rw-r--r--. 1 root root 361 Jan 1 01:24 .bashrc
drwxr-xr-x 3 root root 4096 Jan 1 01:25 .cache/
drwxr-xr-x 3 root root 4096 Jan 1 01:25 .config/
-rw-r--r--. 1 root root 100 Dec 28 2013 .cshrc
-rw-r--r-- 1 root root 0 Apr 17 12:01 garbage.file
-rw-r--r-- 1 root root 0 Apr 17 11:58 important.doc
drwxr-xr-x 2 root root 4096 Apr 17 11:59 Indominus/
drwxr-xr-x 2 root root 4096 Apr 17 11:57 Misc/
-rw------- 1 root root 42 Apr 14 12:44 .my.cnf
-rw-r--r-- 1 root root 0 Apr 17 12:00 probs.xls
drwxr-xr-x 2 root root 4096 Apr 17 11:57 Red Wings/
-rw------- 1 root root 1024 Jan 1 01:22 .rnd
drwxr-xr-x 2 root root 4096 Apr 17 11:56 Spreadsheets/
drw------- 2 root root 4096 Apr 14 12:42 .ssh/
-rw-r--r--. 1 root root 129 Dec 28 2013 .tcshrc
drwxr-xr-x 2 root root 4096 Apr 17 11:57 Work/

In the above case two switches are added: -l and -a. The -l uses the long listing format, and the -a switch lists all of the files, including hidden files.

Each column contains an important bit of information:

Column | Information | Example

  • 1 | Permissions | drwxr-xr-x
  • 2 | # of Hard Links | 2
  • 3 | User That Owns File or Directory | root
  • 4 | Group for File or Directory | root
  • 5 | File Size | 4096
  • 6 | Timestamp | Apr 17 11:59
  • 7 | Filename | Indominus/

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How To Check the Kernel Version in Linux / Ubuntu / CentOS

The following command works with all Linux distributions, such as Red Hat, CentOS, Debian, and Ubuntu. It also works on other UNIX-like operating systems such as HPUX, FreeBSD, OpenBSD, Solaris, etc. Use the following command to check which kernel version your server is currently running:

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