In essence, copying a file on Linux is really simple: use the cp command, followed by the filename-to-be-copied to the filename-to-copy-to. It looks something like this:

reader@ubuntu:~$ ls -l
total 12
-rw-rw-r-- 1 reader reader   69 Jul 14 13:18 nanofile.txt
drwxrwxr-x 2 reader reader 4096 Aug  4 16:16 testdir
-rwxr-xr-- 1 reader reader    0 Aug  4 13:44 testfile
drwxrwx--- 2 reader reader 4096 Aug  4 16:18 umaskdir
-rw-rw---- 1 reader games     0 Aug  4 16:18 umaskfile
reader@ubuntu:~$ cp testfile testfilecopy
reader@ubuntu:~$ ls -l
total 12
-rw-rw-r-- 1 reader reader   69 Jul 14 13:18 nanofile.txt
drwxrwxr-x 2 reader reader 4096 Aug  4 16:16 testdir
-rwxr-xr-- 1 reader reader    0 Aug  4 13:44 testfile
-rwxr-xr-- 1 reader reader    0 Aug 18 14:00 testfilecopy
drwxrwx--- 2 reader reader 4096 Aug  4 16:18 umaskdir
-rw-rw---- 1 reader games     0 Aug  4 16:18 umaskfile
reader@ubuntu:~$

As you can see, in this example we copied an (empty) file that was already owned by us, while we were in the same directory as the file. This might raise some questions, such as:

• Do we always need to be in the same directory as the source and destination file?
• What about the permissions of the file?
• Can we also copy directories with cp?

As you might expect, as with many things under Linux, the cp command is also very versatile. We can indeed copy files not owned by us; we do not need to be in the same directory as the file, and we can also copy directories! Let's try a few of these things out:

reader@ubuntu:~$ cd /var/log/
reader@ubuntu:/var/log$ ls -l
total 3688
<SNIPPED>
drwxr-xr-x  2 root      root               4096 Apr 17 20:22 dist-upgrade
-rw-r--r--  1 root      root             550975 Aug 18 13:35 dpkg.log
-rw-r--r--  1 root      root              32160 Aug 11 10:15 faillog
<SNIPPED>
-rw-------  1 root      root              64320 Aug 11 10:15 tallylog
<SNIPPED>
reader@ubuntu:/var/log$ cp dpkg.log /home/reader/
reader@ubuntu:/var/log$ ls -l /home/reader/
total 552
-rw-r--r-- 1 reader reader 550975 Aug 18 14:20 dpkg.log
-rw-rw-r-- 1 reader reader     69 Jul 14 13:18 nanofile.txt
drwxrwxr-x 2 reader reader   4096 Aug  4 16:16 testdir
-rwxr-xr-- 1 reader reader      0 Aug  4 13:44 testfile
-rwxr-xr-- 1 reader reader      0 Aug 18 14:00 testfilecopy
drwxrwx--- 2 reader reader   4096 Aug  4 16:18 umaskdir
-rw-rw---- 1 reader games       0 Aug  4 16:18 umaskfile
reader@ubuntu:/var/log$ cp tallylog /home/reader/
cp: cannot open 'tallylog' for reading: Permission denied
reader@ubuntu:/var/log$

So, what happened? We used cd to change the directory to /var/log/. We listed the files there using ls with the long option. We copied a file with a relative path that we were able to read, but that was owned by root:root, to the fully qualified /home/reader/ directory. When we listed /home/reader/ with the fully qualified path, we saw that the copied file was now owned by reader:reader. When we tried to do the same for the tallylog file, we got the error cannot open 'tallylog' for reading: Permission denied. This should not be unexpected, since we do not have any read permissions on that file, so copying would be hard.

This should answer two of the three questions. But what about directories? Let's try to copy the /tmp/ directory into our home directory:

reader@ubuntu:/var/log$ cd
reader@ubuntu:~$ cp /tmp/ .
cp: -r not specified; omitting directory '/tmp/'
reader@ubuntu:~$ ls -l
total 552
-rw-r--r-- 1 reader reader 550975 Aug 18 14:20 dpkg.log
-rw-rw-r-- 1 reader reader     69 Jul 14 13:18 nanofile.txt
drwxrwxr-x 2 reader reader   4096 Aug  4 16:16 testdir
-rwxr-xr-- 1 reader reader      0 Aug  4 13:44 testfile
-rwxr-xr-- 1 reader reader      0 Aug 18 14:00 testfilecopy
drwxrwx--- 2 reader reader   4096 Aug  4 16:18 umaskdir
-rw-rw---- 1 reader games       0 Aug  4 16:18 umaskfile
reader@ubuntu:~$ cp -r /tmp/ .
cp: cannot access '/tmp/systemd-private-72bcf47b69464914b021b421d5999bbe-systemd-timesyncd.service-LeF05x': Permission denied
cp: cannot access '/tmp/systemd-private-72bcf47b69464914b021b421d5999bbe-systemd-resolved.service-ApdzhW': Permission denied
reader@ubuntu:~$ ls -l
total 556
-rw-r--r-- 1 reader reader 550975 Aug 18 14:20 dpkg.log
-rw-rw-r-- 1 reader reader     69 Jul 14 13:18 nanofile.txt
drwxrwxr-x 2 reader reader   4096 Aug  4 16:16 testdir
-rwxr-xr-- 1 reader reader      0 Aug  4 13:44 testfile
-rwxr-xr-- 1 reader reader      0 Aug 18 14:00 testfilecopy
drwxrwxr-t 9 reader reader   4096 Aug 18 14:38 tmp
drwxrwx--- 2 reader reader   4096 Aug  4 16:18 umaskdir
-rw-rw---- 1 reader games       0 Aug  4 16:18 umaskfile
reader@ubuntu:~$

For such a simple exercise, a lot actually happened! First, we navigate back to our home directory using cd without any arguments; a neat little trick in itself. Next, we try to copy the entire /tmp/ directory to . (which, as you should remember, is shorthand for current directory). However, this fails with the error -r not specified; omitting directory '/tmp/'. We list the directory to check this, and indeed, it seems like nothing happened. When we add the -r, as specified by the error, and retry the command, we get some Permission denied errors. This is not unexpected, since not all files inside the /tmp/ directory will be readable to us. Even though we got the errors, when we now check the contents of our home directory, we can see the tmp directory there! So, using the -r option, which is short for --recursive, allows us to copy directories and everything that's in them.