We all forget where we put our stuff sometimes; I always forget where I keep my wallet and where I save my files. I am pretty sure that you also forget where you keep your files, and so in this chapter, you will learn two different ways you can use to search and locate files.

The locate command

If you know the name of your file but you are unsure of the file’s location, you can use the locate command to get the file’s path.

The locate command searches for a file location in a prebuilt file database, and thus it’s crucial to update the file database before using the locate command. If you don’t update the database, the locate command may fail to retrieve the location of newly created files.

Updating the file database

To update the file database, you have to run the updatedb command as the root user:

root@ubuntu-linux:~# updatedb

The updatedb command will not display any output.

Now, let’s say we forgot the location of the file facts.txt, and we don’t remember where it is; in this case, you can run the locate command followed by the filename:

root@ubuntu-linux:~# locate facts.txt
/home/elliot/facts.txt
/var/facts.txt

BOOM! It displayed the location of the file facts.txt.

Now I will show you what will happen if you search for a newly created file without updating the file database.

Create an empty file named ghost.txt in the /home directory:

root@ubuntu-linux:/# touch /home/ghost.txt

Now try searching for the file ghost.txt:

root@ubuntu-linux:/# locate ghost.txt 
root@ubuntu-linux:/#

The locate command couldn’t find it! Why is that?........ That’s because you created a new file, and the file database doesn’t know about it yet. You have to run the updatedb command first to update the file database:

root@ubuntu-linux:/# updatedb 
root@ubuntu-linux:/# locate ghost.txt
/home/ghost.txt

YES! After you update the file database, the locate command can now get the location of the file ghost.txt.

You can also use wildcards with the locate command. For example, locate *.log will search for all the log files in your system. You can also use the -r option to enable regex in your search.

The find command

The find command is a much more powerful command you can use to search for files in Linux. Unlike the locate command, the find command runs in real time, so you don’t need to update any file database. The general syntax of the find command is as follows:

find [starting-point(s)] [options] [expression]

The find command will search under each starting-point (directory) you specify.

For example, to search for all the .txt files under your /home directory, you can run:

root@ubuntu-linux:~# find /home -name "*.txt"
/home/elliot/facts2.txt
/home/elliot/dir1/directory2/file1.txt
/home/elliot/dir1/directory2/file3.txt
/home/elliot/dir1/directory2/file2.txt
/home/elliot/soft.txt
/home/elliot/facts.txt
/home/elliot/practise.txt
/home/elliot/upper.txt
/home/elliot/mydate.txt
/home/elliot/all.txt
/home/elliot/Mars.txt
/home/elliot/output.txt
/home/elliot/planets.txt
/home/elliot/error.txt
/home/elliot/animals.txt
/home/ghost.txt

The -name option searches for filename; there are many other options you can use with the find command.
The -type option searches for file type; for example, to search for all the directories in /home/elliot/dir1, you can run:

root@ubuntu-linux:~# find /home/elliot/dir1 -type d
/home/elliot/dir1
/home/elliot/dir1/cities
/home/elliot/dir1/directory2

Notice it only listed the directories in /home/elliot/dir1. To list regular files instead, you can run:

root@ubuntu-linux:~# find /home/elliot/dir1 -type f
/home/elliot/dir1/cities/paris
/home/elliot/dir1/cities/london
/home/elliot/dir1/cities/berlin
/home/elliot/dir1/directory2/file1.txt
/home/elliot/dir1/directory2/file3.txt
/home/elliot/dir1/directory2/file2.txt

To search for both regular files and directories, you can use a comma:

root@ubuntu-linux:~# find /home/elliot/dir1 -type d,f
/home/elliot/dir1
/home/elliot/dir1/cities
/home/elliot/dir1/cities/paris
/home/elliot/dir1/cities/london
/home/elliot/dir1/cities/berlin
/home/elliot/dir1/directory2
/home/elliot/dir1/directory2/file1.txt
/home/elliot/dir1/directory2/file3.txt
/home/elliot/dir1/directory2/file2.txt

Now as the root user create the two files large.txt and LARGE.TXT in /root:

root@ubuntu-linux:~# touch large.txt LARGE.TXT

Let’s say you forgot where these two files are located; in this case, you can use / as your starting-point:

root@ubuntu-linux:~# find / -name large.txt
/root/large.txt

Notice it only listed the location of large.txt. What if you wanted the other file LARGE.TXT as well? In this case, You can use the -iname option, which makes the search case insensitive:

root@ubuntu-linux:~# find / -iname large.txt
/root/LARGE.TXT
/root/large.txt

Let’s append the line "12345" to the file large.txt:

root@ubuntu-linux:~# echo 12345 >> large.txt

Notice the size of the files large.txt and LARGE.txt:

root@ubuntu-linux:~# du -b large.txt LARGE.TXT
6 large.txt
0 LARGE.TXT

The file LARGE.TXT is zero bytes in size because it’s empty. You can use the -size option to search for files based on their size.

For example, to search for empty files under the /root directory, you can run the command:

root@ubuntu-linux:~# find /root -size 0c
/root/LARGE.TXT

As you can see, it listed LARGE.TXT as it has zero characters; 0c means zero characters (or bytes). Now, if you want to search for files of size 6 bytes under /root, you can run:

root@ubuntu-linux:~# find /root -size 6c
/root/large.txt

As you can see, it listed the file large.txt.

You can even use size ranges in your search; Table 16 shows you some examples of using size ranges with the find command.

The -mtime and -atime options search for files based on modification and access times. The -exec is also a useful command option that allows you to run another command on the find results.

For example, you can do a long-listing on all the empty files in /root by running the command:

root@ubuntu-linux:~# find /root -size 0c -exec ls -l {} +
-rw-r--r-- 1 root root 0 May 16 14:31 /root/LARGE.TXT

A lot of people forget to include {} + when using the -exec option; {} + references all the files that are found in the find results.

You can use any command you want with the -exec option. For example, instead of long-listing, you may want to remove the files you get from the find results. In this case, you can run:

root@ubuntu-linux:~# find /root -size 0c -exec rm {} +

Now the file LARGE.TXT is removed:

root@ubuntu-linux:~# ls -l LARGE.TXT
ls: cannot access 'LARGE.TXT': No such file or directory

I highly recommend that you read the find man pages to explore the numerous other options that can be used.

Knowledge check

For the following exercises, open up your Terminal and try to solve the following tasks:

1. Use the locate command to find the path of the file boot.log.
2. Find all the files that are bigger than 50 MB in size.
3. Find all the files that are between 70 MB and 100 MB in size.
4. Find all the files that are owned by the user smurf.
5. Find all the files that are owned by the group developers.