DragonFly On-Line Manual Pages
UNDO(1) DragonFly General Commands Manual UNDO(1)
undo -- Undo changes made to files on HAMMER filesystems
undo [-adDiuv] [-o outfile] [-t transaction-id] [-t transaction-id]
The undo utility acquires an older version of the specified files and can
output them to stdout, generate a file with the previous contents, or
generate a diff to stdout. A history can also be generated.
The options are as follows:
-d Generate a unified diff from the older version to the current
-D Generate a unified diff from the current version to the older
-i Generate a single line giving the transaction id and converted
timestamp of the version of the file requested, rather than dump-
ing the contents of the file.
-a Iterate through the file's entire history generating undo files,
diffs, output, etc. Note that due to the way file creation is
laid down a file may appear to be zero-filled just after creation
before the data is actually synced. There will be a later ver-
sion with the synced data. This is a known bug.
-u Output to a file with name synthesized from the input filename
postfixed with ".undo". If not specified output is either to
stdout or, if a single file argument is given, the file specified
by the -o option.
-v Increase verboseness.
Output to the specified file instead of to stdout. If iterating
through a file's entire history outfile will be postfixed with an
iteration number in the form "outfile.%04d". If multiple files
are specified outfile is used as a template where '%s' is
replaced with the last component of each file path. When used
with multiple files '%%' must be used in the outfile specifica-
tion to indicate a '%'. When used with a single file the outfile
string is used verbatim.
Specify how far to go back in time, by giving a hexadecimal HAM-
MER transaction id which must start with "0x". If not specified
the program will attempt to locate the most recent version of the
file(s) prior to the current version. This option does not apply
if -a is specified.
A second -t specification may be given to provide two end-points
for a diff, and will imply -d unless overridden.
Transaction ids always start with "0x". A simple index may be
specified instead of a transaction id where 0 indicates the lat-
est version and increasing values indicate older versions.
The undo utility exits 0 on success, and >0 if an error occurs.
undo -d mytextfile
undo -o mytextfile.old mytextfile
Warning: fake transaction id path@@0x... While locating past versions of
the file, undo came across a fake transaction id, which are automatically
generated by hammer(5) in case the file's directory entry and inode got
bisected in the past.
The undo utility first appeared in DragonFly 1.13.
Matthew Dillon <email@example.com>
HAMMER only synchronizes information to disk every 30 seconds or so and a
quick file create / delete is done entirely in system memory and cannot
be undone. This can be worked around by running ``hammer synctid
DragonFly 4.7 September 27, 2015 DragonFly 4.7