System Management Guide: Operating System and Devices

Compressing Files

Several methods exist for compressing a file system:

• Use the -p flag with the backup command.
• Use the compress or pack commands.

Files are compressed for the following reasons:

• Saving storage and archiving system resources:
  • Compress file systems before making backups to preserve tape space.
  • Compress log files created by shell scripts that run at night; it is easy to have the script compress the file before it exits.
  • Compress files that are not currently being accessed. For example, the files belonging to a user who is away for extended leave can be compressed and placed into a tar archive on disk or to a tape and later restored.
• Saving money and time by compressing files before sending them over a network.

Procedure

To compress the foo file and write the percentage compression to standard error, type:

compress -v foo

See the compress command for details about the return values but, in general, the problems encountered when compressing files can be summarized as follows:

• The command might run out of working space in the file system while compressing. Because the compress command creates the compressed files before it deletes any of the uncompressed files, it needs extra space-from 50% to 100% of the size of any given file.
• A file might fail to compress because it is already compressed. If the compress command cannot reduce the file size, it fails.