remsync - remotely synchronize file trees
remsync -sxv tree [state-file]
remsync -duxvD tree [state-file [diff-file]]
remsync [-xv] tree [diff-file]
Remsync synchronizes file trees of distant machines, i.e. machines that
do not have a fast network between them. It accomplishes this in three
Create a state file containing a description of the machine to be
Compute a file of differences on the source machine using the state
file to compare the two file trees.
Update the target machine using the data in the differences file.
This process requires that you move two files, a state file from the
target machine to the source machine, and a differences file from the
source machine to the target machine. The state file is an ASCII file
that may be edited, usually to make remsync ignore some files or file
The argument tree may be a single file or a directory. A directory is
traversed recursively. The state-file and diff-file arguments may be of
any file type. The differences file contains an end marker, so it may be
followed by trailing junk. Standard input or output is used if these
arguments are omitted or replaced by a minus sign.
State file format
A state file has a line for each file in a tree. A line looks like this
formally for a simple file:
name mode owner group length date [link-number [last]]
The best way to show how each type of file is represented is by example:
/ d755 0 0
bin d755 2 0
[ 644 2 0 233 759160857 1
cat 755 2 0 3772 768742021
test 755 2 0 233 759160857 1 last
dev d755 0 0
fd0 b666 0 0 200
console c600 10 0 400
sd2 b600 0 0 a02
fifo p700 2 0
opt -> usr/opt
usr ignore (Cross-device link)
The root of the tree is always represented by a /, no matter what type of
file it may be. Directory entries of the root follow at the same level.
Files in subdirectories are indented by two spaces. (Eight spaces are
replaced by a TAB.) Normal files have their length and modified time in
the state file, devices have their device number in hex, etc. If files
are hard linked to each other then they all get an extra "link number" to
bind them together. The last link is marked with the word last.
One usually only modifies a state file to ignore differences between two
files. One does this by replacing the file attributes with the word
ignore. (Remsync generates this keyword too, with the reason why added
-s Generate a state file.
-d Generate a differences file. (The default is to apply a differences
-u Only add new files or update files with newer versions.
-x Do not cross device boundaries. This allows one to operate on the
root file system for instance ignoring the /usr file system.
-D Debug differences file generation. With this flag no file contents
are added to the differences file. The result is then human
-v Lists the commands added to the differences file, or the actions
done applying a differences file. The output looks like UNIX
commands except for the words "add", "restore" and "update"
indicating addition of a new file, replacing a file with an older
version, or replacement by a newer version.
Actions taken by the author to update his notebook "finiah" from his main
finiah# remsync -s /usr /tmp/finiah.state
Edit the state file to ignore .Xauthority files and /usr/var.
finiah# tar cvf /dev/fd0 /tmp/finiah.state
darask# tar xvf /dev/fd0
darask# remsync -dv /usr /tmp/finiah.state | vol 1440 /dev/fd0
finiah# vol 1440 /dev/fd0 | remsync -v /usr
One could add a file compression/decompression program between remsync
and vol, to reduce the number of floppies to move about, but that
actually slows things down! (Note that one only needs to shuffle two
floppies about if the two machines are adjacent. To update a remote
machine it does make sense to use compression to reduce the number of
floppies to carry.)
synctree(1), vol(1), tar(1).
Nothing stops you from using remsync over a fast network of course.
Synctree can be a bit tedious if you only want to ignore a few files.
Editing a state file is then easier.
Files are overwritten, not removed, when they are updated. This means
that links outside the tree are also updated. The less desirable
alternative to this is to break the link before the update.
The verbose option may say that a link is to be created when making a
differences file. The link is often already there when the update takes
place, so no action is taken, and thus no talk about it. So you may miss
a few mutterings about links if you compare the messages.
Kees J. Bot (email@example.com)