How to find the location of commands in Linux?

This post is for those who use the various commands available in Linux but they are not exactly aware of the location of those commands.

Basically those commands we use in Linux are configured in binary language. If you try to read any of those files using any editor then you won't understand any thing as it is not human readable. These all commands are installed along with the relative packages with the installation of OS.
But well returning to the topic as most of us know that mostly all the required commands are placed in /bin, /usr/bin, /sbin and /usr/sbin.

But how do you check whether the command you are using is in which of the above location. The first method would be you manually search in all those locations using any of the find command.

Secondly you can use which command, It will show you the location of the command along with alias entry if any assigned for that command.

# which "command_name"

For eg:

# which cp
alias cp='cp -i'

# which useradd
In case you get the below error# which samba
no samba in (/usr/lib/qt-3.3/bin:/usr/local/sbin
It means your PATH variable does not contains the path for samba command. In that case which will not help you find the location of the command.

So, you can use the below command for the same purpose
# whereis command_name
For example
# whereis useradd
useradd: /usr/sbin/useradd /usr/share/man/man8/useradd.8.gz

I hope I made my self clear

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