Master Linux File Search: Using which, whereis, and locate Commands

which command

The which command searches the directories listed in the PATH environment variable for the first occurrence of a specified executable and returns its full path.

Syntax: which <executable_name> Common options (though rarely needed) include: -n – specify minimum filename length (rarely used). -p – include the full path in the output. -w – set output column width. -V – display version information.

Example 1 – Find the path of a command:

which lsmod
# /usr/bin/lsmod

which pwd
# /bin/pwd

which adduser
# /usr/sbin/adduser

Explanation: which looks only in the directories defined by PATH, so results vary with different PATH configurations.

Example 2 – Locate the which command itself:

which which
# alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde'
# /usr/bin/which

Note: The first line shows that which is aliased; the real binary resides at /usr/bin/which.

Example 3 – Search for a built‑in command ( cd ):

which cd
# (no output)

Reason: cd is a shell built‑in, not an external executable, so which cannot find it.

whereis command

The whereis utility locates the binary, source, and manual page files for a given command. It queries a pre‑built database, making it faster than find, but the database is updated only periodically (typically weekly).

Syntax: whereis [-bmsu] [-B path] [-M path] [-S path] filename Key options: -b – search for binaries only. -m – search for manual pages. -s – search for source files. -u – search for files not matching the above categories. -B – specify alternate binary search path. -M – specify alternate manual page search path. -S – specify alternate source search path.

Example – Find all related files for svn :

whereis svn
# svn: /usr/bin/svn /usr/local/svn /usr/share/man/man1/svn.1.gz

Example – Retrieve only binaries for svn :

whereis -b svn
# svn: /usr/bin/svn /usr/local/svn

Example – Retrieve only manual pages for svn :

whereis -m svn
# svn: /usr/share/man/man1/svn.1.gz

Because the database may be outdated, results can include files that have been removed or miss newly created ones until the next update.

locate command

The locate command searches a system‑wide index (maintained by updatedb ) for file names matching a pattern. It is extremely fast compared to find , but may miss very recent files if the index has not been refreshed. Syntax: locate [options] pattern Important options: -e – exclude matches. -1 – safe mode (hide files without read permission). -f – exclude a specific filesystem from the index. -q – quiet mode (suppress errors). -n N – limit output to N results. -r regex – use a regular expression. -o file – specify an alternate database file. -d path – specify the path to the database. -h – display help. -V – display version.

Example 1 – Find all paths containing pwd :

locate pwd
# /bin/pwd
# /etc/.pwd.lock
# /sbin/unix_chkpwd
# /usr/bin/pwdx
# ... (other matches)

Example 2 – Search for files in /etc that start with sh :

locate /etc/sh
# /etc/shadow
# /etc/shadow-
# /etc/shells

Example 3 – Search for files in /etc that start with m :

locate /etc/m
# /etc/magic
# /etc/magic.mime
# /etc/mailcap
# /etc/mailcap.order
# /etc/manpath.config
# /etc/mate-settings-daemon

Note: Because locate relies on the index, newly created or renamed files may not appear until updatedb runs (usually via a daily cron job).