GNU cpio is a tool for creating and extracting archives, or copying files from one place to another. It handles many cpio formats as well as reading and writing tar files.

The following archive formats are supported: binary, old ASCII, new ASCII, CRC, HP-UX binary, HP-UX old ASCII, old tar, and POSIX.1 tar. The tar format is provided for compatibility with the tar program. By default, cpio creates binary format archives, for compatibility with older cpio programs. When extracting from archives, cpio automatically recognizes which kind of archive it is reading and can read archives created on machines with a different byte-order.

Copy-Out Mode Syntax:

In copy-out mode, cpio copies files into an archive. It reads a list of filenames, one per line, on the standard input and writes the archive onto the standard output. A typical way to generate the list of filenames is with the find command; you should give find the -depth option to minimize problems with permissions on directories that are unreadable. Copy-Out mode syntax:

cpio {-o|--create} [-0acvABLV] [-C bytes] [-H format] [-M message] 
     [-O [[user@]host:]archive] [-F [[user@]host:]archive] 
     [--file=[[user@]host:]archive] [--format=format] 
     [--message=message][--null] [--reset-access-time] [--verbose] [--dot] 
     [--append] [--block-size=blocks] [--dereference] [--io-size=bytes] 
     [--rsh-command=command] [--help] [--version] < name-list [> archive]

Copy-In Mode Syntax:

In copy-in mode, cpio copies files out of an archive or lists the archive contents. It reads the archive from the standard input. Any non-option command line arguments are shell globbing patterns; only files in the archive whose names match one or more of those patterns are copied from the archive. Unlike in the shell, an initial '.' in a filename does match a wildcard at the start of a pattern, and a '/' in a filename can match wildcards. If no patterns are given, all files are extracted. Copy-In mode syntax:

cpio {-i|--extract} [-bcdfmnrtsuvBSV] [-C bytes] [-E file] [-H format] 
     [-M message] [-R [user][:.][group]] 
     [-I [[user@]host:]archive] [-F [[user@]host:]archive] 
     [--file=[[user@]host:]archive] [--make-directories] [--nonmatching] 
     [--preserve-modification-time] [--numeric-uid-gid] [--rename] [-t|--list] 
     [--swap-bytes] [--swap] [--dot] [--unconditional] [--verbose] 
     [--block-size=blocks] [--swap-halfwords] [--io-size=bytes] 
     [--pattern-file=file] [--format=format] [--owner=[user][:.][group]] 
     [--no-preserve-owner] [--message=message] [--force-local] 
     [--no-absolute-filenames] [--absolute-filenames] [--sparse] 
     [--only-verify-crc] [--to-stdout] [--quiet] [--rsh-command=command] 
     [--help] [--version] [pattern...] [< archive]

Copy-Pass Mode Syntax:

In copy-pass mode, cpio copies files from one directory tree to another, combining the copy-out and copy-in steps without actually using an archive. It reads the list of files to copy from the standard input; the directory into which it will copy them is given as a non-option argument. Copy-Pass mode syntax:

cpio {-p|--pass-through} [-0adlmuvLV] [-R [user][:.][group]] [--null] 
     [--reset-access-time] [--make-directories] [--link] [--quiet] 
     [--preserve-modification-time] [--unconditional] [--verbose] [--dot] 
     [--dereference] [--owner=[user][:.][group]] [--no-preserve-owner] 
     [--sparse] [--help] [--version] destination-directory < name-list

Options

When creating an archive, cpio takes the list of files to be processed from the standard input, and then sends the archive to the standard output, or to the device defined by the '-F' option. Usually find or ls is used to provide this list to the standard input. In the following example you can see the possibilities for archiving the contents of a single directory:

% ls | cpio -ov > directory.cpio

The '-o' option creates the archive, and the '-v' option prints the names of the files archived as they are added. Notice that the options can be put together after a single '-' or can be placed separately on the command line. The '>' redirects the cpio output to the file 'directory.cpio'.

If you wanted to archive an entire directory tree, the find command can provide the file list to cpio:

% find . -print -depth | cpio -ov > tree.cpio

This takes all the files in the current directory, the directories below and place them in the archive tree.cpio. Again the '-o' creates an archive, and the '-v' option shows you the name of the files as they are archived (see 'Copy-out mode'). Using the '.' in the find statement gives you more flexibility when doing restores, as it will save file names with a relative path via a hard-wired, absolute path. The '-depth' option forces 'find' to print of the entries in a directory before printing the directory itself. This limits the effects of restrictive directory permissions by printing the directory entries in a directory before the directory name itself.

Extracting an archive requires a bit more thought because cpio will not create directories by default. Another characteristic, is it will not overwrite existing files unless specified.

% cpio -iv < directory.cpio

This will retrieve the files archived in the file directory.cpio and place them in the present directory. The '-i' option extracts the archive and the '-v' shows the file names as they are extracted. If you are dealing with an archived directory tree, you need to use the '-d' option to create directories as necessary, something like:

% cpio -idv < tree.cpio

This takes the contents of the archive tree.cpio and extract it to the current directory. If you try to extract the files on top of files of the same name that already exist (and have the same or later modification time) cpio will not extract the file unless told to do so by the -u option (see 'Copy-in mode').

In copy-pass mode, cpio copies files from one directory tree to another, combining the copy-out and copy-in steps without actually using an archive. It reads the list of files to copy from the standard input; the directory into which it will copy them is given as a non-option argument (see 'Copy-pass mode').

% find . -depth -print0 | cpio --null -pvd new-dir

The example shows copying the files of the present directory, and sub-directories to a new directory called new-dir. Some new options are the '-print0' available with GNU find, combined with the '--null' option of cpio. These two options act together to send file names between find and cpio, even if special characters are embedded in the file names. Another is '-p', which tells cpio to pass the files it finds to the directory 'new-dir'.

find . -print | cpio -ocv > /dev/fd0

Above, using the find command would list all files and directories and using the cpio command copy those files listed to the floppy drive.

find . -print | cpio -dumpv /home/users/hope

In the above example, the find command would list all files and subdirectories of the current directory, and pipe them to the cpio command, which copies those files to the hope user account.

cpio -icuvd < /dev/fd0

The above command would restore the files back from the floppy.