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Migrating Data and Keeping Data Synchronized with Rsync

RSYNC is a powerful tool for moving or syncing data between server. It is NOT, however, an effective tool for keeping data up to date continuously or keeping data synchronized in both directions.

How it works

RSYNC works by looking at data on the source and then comparing it with the destination. On a simple level, rsync will look at the metadata of a file to decide whether a file qualifies for backing up. This will typically be the archive bit, time stamp or other data.

Optionally, rsync can run a comparison between files by running a hash sum on the file on both the source and the destination and then comparing the hashes. This can be useful for backing up files which don't adjust their time stamp or archive bit like you will find with databases.

Additionally, on file systems that support it, rsync can be used to compare data on the receiving end of the sync to a different directory and creating hard links between those two directories. This means that you can have a complete backup of a folder structure and then create a new backup and every file which is unchanged between the two will be hard linked together. This results in an entire directory structure as a backup but with only the new and 'changed' files being transferred.

Examples

In this example. If you want to use rsync to copy individual files or groups of files from one directory to another:

rsync -v /path/to/source/file.txt /path/to/destination/directory/
rsync -v /path/to/source/files*.txt /path/to/destination/directory/

To copy an entire directory tree or several directories with a wildcard:

rsync -av /path/to/source/directory /path/to/destination/directory
rsync -av /path/to/source/directory* /path/to/destination/
rsync -av /path/to/source/* /path/to/destination/

To copy a directory using on top of an existing directory to bring it up to date (please note that the –delete flag will remove files on the destination that have been also removed from the source since the last sync. This is useful to create a true snapshot of files that are supposed to be deleted):

rsync -av --delete /path/to/source/* /path/to/destination/

RSYNC is useful over SSH as well. Here we can use ssh for secure syncs between servers:

rsync -av root@hostname_or_IP_of_source:/path/to/source/* /path/to/destination/

To backup using a different directory and use hard links here is an example:

rsync -avH --link-dest=/path/to/previousbackup/ /path/to/source/* /path/to/destination/

Useful Switches

        -v, --verbose               increase verbosity
        -q, --quiet                 suppress non-error messages
            --no-motd               suppress daemon-mode MOTD (see caveat)
        -c, --checksum              skip based on checksum, not mod-time & size
        -a, --archive               archive mode; same as -rlptgoD (no -H)
            --no-OPTION             turn off an implied OPTION (e.g. --no-D)
        -r, --recursive             recurse into directories
        -R, --relative              use relative path names
            --no-implied-dirs       don't send implied dirs with --relative
        -b, --backup                make backups (see --suffix & --backup-dir)
            --backup-dir=DIR        make backups into hierarchy based in DIR
            --suffix=SUFFIX         backup suffix (default ~ w/o --backup-dir)
        -u, --update                skip files that are newer on the receiver
            --inplace               update destination files in-place
            --append                append data onto shorter files
        -d, --dirs                  transfer directories without recursing
        -l, --links                 copy symlinks as symlinks
        -L, --copy-links            transform symlink into referent file/dir
            --copy-unsafe-links     only "unsafe" symlinks are transformed
            --safe-links            ignore symlinks that point outside the tree
        -k, --copy-dirlinks         transform symlink to dir into referent dir
        -K, --keep-dirlinks         treat symlinked dir on receiver as dir
        -H, --hard-links            preserve hard links
        -p, --perms                 preserve permissions
            --executability         preserve executability
            --chmod=CHMOD           affect file and/or directory permissions
        -o, --owner                 preserve owner (super-user only)
        -g, --group                 preserve group
            --devices               preserve device files (super-user only)
            --specials              preserve special files
        -D                          same as --devices --specials
        -t, --times                 preserve times
        -O, --omit-dir-times        omit directories when preserving times
            --super                 receiver attempts super-user activities
        -S, --sparse                handle sparse files efficiently
        -n, --dry-run               show what would have been transferred
        -W, --whole-file            copy files whole (without rsync algorithm)
        -x, --one-file-system       don't cross filesystem boundaries
        -B, --block-size=SIZE       force a fixed checksum block-size
        -e, --rsh=COMMAND           specify the remote shell to use
            --rsync-path=PROGRAM    specify the rsync to run on remote machine
            --existing              skip creating new files on receiver
            --ignore-existing       skip updating files that exist on receiver
            --remove-source-files   sender removes synchronized files (non-dir)
            --del                   an alias for --delete-during
            --delete                delete extraneous files from dest dirs
            --delete-before         receiver deletes before transfer (default)
            --delete-during         receiver deletes during xfer, not before
            --delete-after          receiver deletes after transfer, not before
            --delete-excluded       also delete excluded files from dest dirs
            --ignore-errors         delete even if there are I/O errors
            --force                 force deletion of dirs even if not empty
            --max-delete=NUM        don't delete more than NUM files
            --max-size=SIZE         don't transfer any file larger than SIZE
            --min-size=SIZE         don't transfer any file smaller than SIZE
            --partial               keep partially transferred files
            --partial-dir=DIR       put a partially transferred file into DIR
            --delay-updates         put all updated files into place at end
        -m, --prune-empty-dirs      prune empty directory chains from file-list
            --numeric-ids           don't map uid/gid values by user/group name
            --timeout=TIME          set I/O timeout in seconds
        -I, --ignore-times          don't skip files that match size and time
            --size-only             skip files that match in size
            --modify-window=NUM     compare mod-times with reduced accuracy
        -T, --temp-dir=DIR          create temporary files in directory DIR
        -y, --fuzzy                 find similar file for basis if no dest file
            --compare-dest=DIR      also compare received files relative to DIR
            --copy-dest=DIR         ... and include copies of unchanged files
            --link-dest=DIR         hardlink to files in DIR when unchanged
        -z, --compress              compress file data during the transfer
            --compress-level=NUM    explicitly set compression level
        -C, --cvs-exclude           auto-ignore files in the same way CVS does
        -f, --filter=RULE           add a file-filtering RULE
        -F                          same as --filter='dir-merge /.rsync-filter'
                                    repeated: --filter='- .rsync-filter'
            --exclude=PATTERN       exclude files matching PATTERN
            --exclude-from=FILE     read exclude patterns from FILE
            --include=PATTERN       don't exclude files matching PATTERN
            --include-from=FILE     read include patterns from FILE
            --files-from=FILE       read list of source-file names from FILE
        -0, --from0                 all *from/filter files are delimited by 0s
            --address=ADDRESS       bind address for outgoing socket to daemon
            --port=PORT             specify double-colon alternate port number
            --sockopts=OPTIONS      specify custom TCP options
            --blocking-io           use blocking I/O for the remote shell
            --stats                 give some file-transfer stats
        -8, --8-bit-output          leave high-bit chars unescaped in output
        -h, --human-readable        output numbers in a human-readable format
            --progress              show progress during transfer
        -P                          same as --partial --progress
        -i, --itemize-changes       output a change-summary for all updates
            --out-format=FORMAT     output updates using the specified FORMAT
            --log-file=FILE         log what we're doing to the specified FILE
            --log-file-format=FMT   log updates using the specified FMT
            --password-file=FILE    read password from FILE
            --list-only             list the files instead of copying them
            --bwlimit=KBPS          limit I/O bandwidth; KBytes per second
            --write-batch=FILE      write a batched update to FILE
            --only-write-batch=FILE like --write-batch but w/o updating dest
            --read-batch=FILE       read a batched update from FILE
            --protocol=NUM          force an older protocol version to be used
            --checksum-seed=NUM     set block/file checksum seed (advanced)
        -4, --ipv4                  prefer IPv4
        -6, --ipv6                  prefer IPv6
        -E, --extended-attributes   copy extended attributes, resource forks
            --cache                 disable fcntl(F_NOCACHE)
            --version               print version number
       (-h) --help                  show this help (see below for -h comment)
content/en_us/kb_o_migrating_data_and_keeping_data_synchronized_with_rsync.txt · Last modified: 2016/07/20 09:04 by dloper

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