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Unix find tutorial

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Part 9: Using find for backups

The find command lets you copy the entire contents of a directory while preserving the permissions, times, and ownership of every file and subdirectory. Because find capabilities to specify complex criteria for files it can create a perfect list of files for cpio, tar, pax and another archiver to backup

Fortunately find has several options that are very useful for structuring the backup:

• -mount Don't descend directories on other filesystems. An alternate name for -xdev, for compatibility with some other versions of find.
• -fstype type File is on a filesystem of type type. The valid filesystem types vary among different versions of Unix; an incomplete list of filesystem types that are accepted on some version of Unix or another is: ufs, 4.2, 4.3, nfs, tmp, mfs, S51K, S52K. You can use -printf with the %F directive to see the types of your filesystems.
• -type c File is of type c:
  
  • b block (buffered) special
  • c character (unbuffered) special
  • d directory
  • p named pipe (FIFO)
  • f regular file
  • l symbolic link; this is never true if the -L option or the
    -follow option is in effect, unless the symbolic link is
    broken. If you want to search for symbolic links when -L
    is in effect, use -xtype.
  • s socket
  • D door (Solaris)

The typical usage is to combine find and the cpio command, as the latter accepts the list of files via standard input.  Tar can do this too with -T - option.  Typically each mount point is backed up in a separate tar or cpio archive. 

cd /usr

find /usr -mount fstype ext3 - | cpio -pdumv /backup/usr080124.cpi

or, using tar:

find /usr -mount fstype ext3 -print0 | tar -null -cvzf /backup/usr080124.tgz

find /usr -newer /backup/usr080124.tgz -mount fstype ext3 -print0 | tar -null -cvzf /backup/usr_delta080124.tgz

You can also try to avoid errors in backing up named pipes, devises, etc  using more complex traversal expressions, for example

find / -mount -fstype ext3 \( -type f -or -type l \) > /tmp/root_list.txt

The problem here is with hard linked files. That that is problem of tar not find. The cpio command is a more sophisticated backup tool than tar. It is harder to use, but is capable of copying special files (such as devices and links) consistently, and will accept wildcard characters when listing the files to be archived.

On higher level you might benefit from exclusion of all files that are not changes in RPMs from which system was installed.  This is the approach taken by  backup built-in in YAST (it uses tar, not cpio). While tar cannot accept the list of files as standard input it has the -T option which can be used to specify the location of file with list of files to be tarred". Here is how this option is described in the manual:

Instead of giving the names of files or archive members on the command line, you can put the names into a file, and then use the ‘--files-from=file-of-names’ (‘-T file-of-names’) option to tar. Give the name of the file which contains the list of files to include as the argument to ‘--files-from’. In the list, the file names should be separated by newlines. You will frequently use this option when you have generated the list of files to archive with the find utility. 

... ... ...

In the file list given by ‘-T’ option, any file name beginning with ‘-’ character is considered a tar option and is processed accordingly.(14) For example, the common use of this feature is to change to another directory by specifying ‘-C’ option:

$ cat list
-C/etc
passwd
hosts
-C/lib
libc.a
$ tar -c -f foo.tar --files-from list

For example if we want to archive file that has size less then 1000 we can first create of list of such files using find and then use tar to created an archive.

find .  -size -1K -print > /etc/small-files
tar -cvzT /etc/small-files -f little.tgz

You can also compress the archive with gzip of the fly:

tar -zPvcf backup.tar.gz -T list_of_files_to_be_tarred_or_list_of_locations

You will want to use the ‘--label=archive-label’ (‘-V archive-label’) option to give the archive a volume label, so you can tell what this archive is even if the label falls off the tape, or anything like that.

Unless the file system you are dumping is guaranteed to fit on one volume, you might need to use the ‘--multi-volume’ (‘-M’) option.

Like find,  tar has an option of that prevent it from crossing the filesystem (partition) boundaries:  ‘--one-file-system’ option to prevent  from crossing file system boundaries when storing (sub)directories.

It also has the ‘--incremental’ (‘-G’) option  (see section Using tar to Perform Incremental Dumps).