If you ever need to use tar to create a backup of either a file or a last two files:

[donnie@localhost ~]$ cd perm_demo_dir
[donnie@localhost perm_demo_dir]$ ls -l
total 0
-rw-rw-r--. 1 donnie accounting 0 Nov  5 20:17 file1.txt
-rw-rw-r--. 1 donnie accounting 0 Nov  5 20:17 file2.txt
-rw-rw-r--. 1 donnie accounting 0 Nov  5 20:17 file3.txt
-rw-rw-r--. 1 donnie accounting 0 Nov  5 20:17 file4.txt
-rw-rw----+ 1 donnie donnie     0 Nov  9 15:19 frank_file.txt
-rw-rw----+ 1 donnie donnie     0 Nov 12 12:29 new_file.txt
[donnie@localhost perm_demo_dir]$

Now, I'll do the backup without --acls:

[donnie@localhost perm_demo_dir]$ cd
[donnie@localhost ~]$ tar cJvf perm_demo_dir_backup.tar.xz perm_demo_dir/
perm_demo_dir/
perm_demo_dir/file1.txt
perm_demo_dir/file2.txt
perm_demo_dir/file3.txt
perm_demo_dir/file4.txt
perm_demo_dir/frank_file.txt
perm_demo_dir/new_file.txt
[donnie@localhost ~]$

It looks good, right? Ah, but looks can be deceiving. Watch what happens when I delete the directory, and then restore it from the backup:

[donnie@localhost ~]$ rm -rf perm_demo_dir/

[donnie@localhost ~]$ tar xJvf perm_demo_dir_backup.tar.xz
perm_demo_dir/
. . .
[donnie@localhost ~]$ cd perm_demo_dir/
[donnie@localhost perm_demo_dir]$ ls -l
total 0
-rw-rw-r--. 1 donnie donnie 0 Nov 5 20:17 file1.txt
-rw-rw-r--. 1 donnie donnie 0 Nov 5 20:17 file2.txt
-rw-rw-r--. 1 donnie donnie 0 Nov 5 20:17 file3.txt
-rw-rw-r--. 1 donnie donnie 0 Nov 5 20:17 file4.txt
-rw-rw----. 1 donnie donnie 0 Nov 9 15:19 frank_file.txt
-rw-rw----. 1 donnie donnie 0 Nov 12 12:29 new_file.txt
[donnie@localhost perm_demo_dir]$

I don't even have to use getfacl to see that the ACLs are gone from the perm_demo_dir directory and all of its files, because the + signs are now gone from them. Now, let's see what happens when I include the --acls option. First, I'll show you that an ACL is set for this directory and its only file:

[donnie@localhost ~]$ ls -ld new_perm_dir
drwxrwxr-x+ 2 donnie donnie 26 Nov 13 14:01 new_perm_dir

[donnie@localhost ~]$ ls -l new_perm_dir
total 0
-rw-------+ 1 donnie donnie 0 Nov 13 14:01 new_file.txt
[donnie@localhost ~]$

Now, I'll use .tar with --acls:

[donnie@localhost ~]$ tar cJvf new_perm_dir_backup.tar.xz new_perm_dir/ --acls
new_perm_dir/
new_perm_dir/new_file.txt
[donnie@localhost ~]$

I'll now delete the new_perm_dir directory and restore it from backup. Again, I'll use the --acls option:

[donnie@localhost ~]$ rm -rf new_perm_dir/

[donnie@localhost ~]$ tar xJvf new_perm_dir_backup.tar.xz --acls
new_perm_dir/
new_perm_dir/new_file.txt

[donnie@localhost ~]$ ls -ld new_perm_dir
drwxrwxr-x+ 2 donnie donnie 26 Nov 13 14:01 new_perm_dir

[donnie@localhost ~]$ ls -l new_perm_dir
total 0
-rw-------+ 1 donnie donnie 0 Nov 13 14:01 new_file.txt
[donnie@localhost ~]$

The presence of the + signs indicates that the ACLs did survive the backup-and-restore procedure. The one slightly tricky part about this is that you must use --acls for both the backup and the restoration. If you omit the option either time, you will lose your ACLs.