The s3qlcp command — S3QL 5.2.3 documentation

# The s3qlcp command

## Synopsis

    s3qlcp [options] <source-dir> <dest-dir>

## Description

The s3qlcp command duplicates the directory tree `source-dir` into `dest-dir` without physically copying the file contents. Both source and destination must lie inside the same S3QL file system.

The replication will not take any additional space for the file contents. Metadata usage will increase proportional to the amount of directory entries and inodes. Only if one of directories is modified later on, the modified data will take additional storage space.

`s3qlcp` can only be called by the user that mounted the file system and (if the file system was mounted with `--allow-other` or `--allow-root`) the root user.

After the replication, both source and target directory will still be completely ordinary directories. You can regard `<src>` as a snapshot of `<target>` or vice versa. However, the most common usage of `s3qlcp` is to regularly duplicate the same source directory, say `documents`, to different target directories. For a e.g. monthly replication, the target directories would typically be named something like `documents_January` for the replication in January, `documents_February` for the replication in February etc. In this case it is clear that the target directories should be regarded as snapshots of the source directory.

Exactly the same effect could be achieved by an ordinary copy program like `cp -a`. However, this procedure would be orders of magnitude slower, because `cp` would have to read every file completely (so that S3QL had to fetch all the data over the network from the backend) before writing them into the destination folder (at which point S3QL would de-duplicate the data).

### Snapshotting vs Hardlinking

Snapshot support in S3QL is inspired by the hardlinking feature that is offered by programs like rsync or storeBackup. These programs can create a hardlink instead of copying a file if an identical file already exists in the backup. However, using hardlinks has disadvantages:

- backups and restores always have to be made with a special program that takes care of the hardlinking. The backups must not be touched by any other programs (they may make changes that inadvertently affect other hardlinked files)

- special care needs to be taken to handle files which are already hardlinked (the restore program needs to know that the hardlink was not introduced by the backup program)

S3QL snapshots do not have these problems, and they can be used with any backup program.

## Options

The s3qlcp command accepts the following options:

> `--log <target>`

>   Destination for log messages. Specify `none` for standard output or `syslog` for the system logging daemon. Anything else will be interpreted as a file name. Log files will be rotated when they reach 1 MiB, and at most 5 old log files will be kept. Default: `None`

> `--debug-modules <modules>`

>   Activate debugging output from specified modules (use commas to separate multiple modules, ‘all’ for everything). Debug messages will be written to the target specified by the `--log` option.

> `--debug`

>   Activate debugging output from all S3QL modules. Debug messages will be written to the target specified by the `--log` option.

> `--quiet`

>   be really quiet

> `--version`

>   just print program version and exit

## Exit Codes

s3qlcp may terminate with the following exit codes:

0:

  Everything went well.

1:

  An unexpected error occurred. This may indicate a bug in the program.

2:

  Invalid command line argument or configuration file key.

## See Also

The S3QL homepage is at https://github.com/s3ql/s3ql/.

The full S3QL documentation should also be installed somewhere on your system, common locations are `/usr/share/doc/s3ql` or `/usr/local/doc/s3ql`.