Unison

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References


Unison also has built-in help:

unison -help               # Brief help
unison -doc topics         # Get list of details documentation
unison -doc all            # Get the whole manual

Alternatives to Unison

Basic usage

  • Synchronize two directories
unison <dir-a> <dir-b>
  • Selecting files to synchronize
    • Synchronize home directory, using Ignore facility to skip some files.
    • Create a subdirectory called shared, and synchronize that directory only.
    • (Linux only) Create a subdirectory called shared, with symbolic links to other local directories, and synchronize that directory only using follow (making symlink transparent).
    • Synchronize home directory as root, using -path switch on the command line:
      unison /home/username ssh://remotehost//home/username -path shared
      

      The -path option can be used as many times as needed, to synchronize several files or subdirectories:

      unison /home/username ssh://remotehost//home/username \
          -path shared \
          -path pub \
          -path .netscape/bookmarks.html
      

      These -path arguments can also be put in your preference file.

Limitation

  • (from the manual) Unison does not understand hardlinks. So copying a repo with hardlinks will just create a new repo where all hard-links are unique (unlinked) copies.

Configuration tips

  • On Samba / CIFS file system, ignore permissions:
perms = 0
In some cases, you also need to use the preferences dontchmod.
  • When running unison with ssh, uses servercmd if unison is not found in the path:
servercmd = /usr/bin/unison

Basic Profile

Here we assume that all profiles will include the default one. If not, a more complex solution is to create a file .unison/common-prefs, that would be included by all profiles, including the default one.

Here a basic setup to backup pen usb stick on Cygwin:

Compile from sources

Compile on powerpc/arm

References:

  • Instructions from Tom Booschaert ([1]).

These are instructions to compile unison from sources on NAS devices with powerpc/arm cpu, and using ipkg package management.

# install OCaml, Gnu C Compiler en Make:
ipkg install ocaml
ipkg install gcc
ipkg install make

# get Unison source and unpack:
wget http://www.seas.upenn.edu/~bcpierce/unison//download/releases/stable/unison-2.32.52.tar.gz
# Other versions:
# wget http://www.seas.upenn.edu/~bcpierce/unison//download/releases/unison-2.27.57/unison-2.27.57.tar.gz
# wget http://www.seas.upenn.edu/~bcpierce/unison//download/releases/unison-2.40.102/unison-2.40.102.tar.gz
tar -xzf unison-2.32.52.tar.gz

# use make to compile:
cd unison-2.32.52
make NATIVE=false UISTYLE=text

# copy executable to bin folder so it can be executed anywhere:
cp unison /opt/bin/
Compilation error
  • Error /bin/sh: etags: not found can be freely ignored.
  • When building with ocaml 3.12, we get the following error:
ocamlc -I lwt -I ubase -custom -g -c /root/build/tmp/unison-2.27.57/update.ml
File "/root/build/tmp/unison-2.27.57/update.ml", line 1, characters 0-1:
Error: The implementation /root/build/tmp/unison-2.27.57/update.ml
       does not match the interface update.cmi:
       Modules do not match:
This is a known bug. Patch file update.mli as follows (see [2]):
sed -ri '/^module NameMap : Map/s/Map.S/MyMap.S/' update.mli
  • On ARM, we had the following error:
+ gcc -o 'unison'   '-Llwt' '-Lubase' '-L/opt/lib/ocaml'  '/tmp/camlprimed354e.c' '-lcamlstr' '-lunix' '-lutil' 'osxsupport.o' 'pty.o' '-lcamlrun' 
-I'/opt/lib/ocaml' -lm  -ldl  -lpthread
/opt/lib/gcc/arm-none-linux-gnueabi/4.2.3/../../../../arm-none-linux-gnueabi/bin/ld: Warning: /lib/libc.so.6: Unknown EABI object attribute 44
/opt/lib/gcc/arm-none-linux-gnueabi/4.2.3/../../../../arm-none-linux-gnueabi/lib/libdl.so: undefined reference to `_dl_tls_get_addr_soft@GLIBC_PRIVATE'
To fix it we temporarily link to a different libdl.so library [3]:
mv /opt/arm-none-linux-gnueabi/lib/libdl.so /opt/arm-none-linux-gnueabi/lib/libdl.so.old
ln -s /lib/libdl.so.2 /opt/arm-none-linux-gnueabi/lib/libdl.so
# Compile Unison with the new library:
make NATIVE=false UISTYLE=text
# Restore the library link
mv /opt/arm-none-linux-gnueabi/lib/libdl.so.old /opt/arm-none-linux-gnueabi/lib/libdl.so
test Unison
unison -version
# unison version 2.27.57
unison -selftest
# Contacting server...
# Connected [//Mnemosyne//root/test-a.tmp -> //Mnemosyne//root/test-b.tmp]
# Running internal tests...
# backups 1 (local)...
# backups 2...
# backups 2a...
# backups 3...
# backups 4...
# backups 5 (directories)...
# backups 6 (backup prefix/suffix)...
# links 1 (directories and links)...
# links 2 (symlink to nowhere)...
# Success :-)