Unison同步时文件属主、组及权限异常变更问题排查

问题现象 #

在Windows 10与Debian 12之间使用Unison 2.53.3同步文件后，Debian端文件的属主、用户组及权限出现异常变更：

同步前Debian端文件信息：

-rw-rw---- 1 www-data www-data 7448 Nov 30 09:13 trac.ini

同步后Debian端文件信息：

-rw-r--r-- 1 thomas  thomas  7447 Nov 30 09:24 trac.ini

执行同步的用户thomas属于www-data用户组，当前Unison配置如下：

owner = false 
group = false
dontchmod = true
perms=0
acl = false

补充推测与同步日志 #

2023-12-01补充推测：Unison通过创建临时文件→删除原文件→重命名临时文件的流程完成同步，新创建的临时文件会继承运行Unison的用户thomas的默认属主、用户组及权限，最终替换原文件后覆盖了原有属性。

同步日志如下：

Unison 2.53.3 (ocaml 4.14.0) started propagating changes at 12:17:50.57 on 30 Nov 2023
[BGN] Updating file trac/conf/trac.ini from D:/ServerSync/www to //debian12//home/www
[files] copy D:/ServerSync/www trac/conf/trac.ini ---> //debian12//home/www trac/conf/trac.ini
[update] updateArchive D:/ServerSync/www trac/conf/trac.ini
[pred] ignore 'trac/conf/trac.ini' = false
[files] copyRec trac/conf/trac.ini ---> .unison.trac.ini.3cf645660f038354c49973b861281767.unison.tmp  (really to trac.ini)
[abort] Checking line 0
[copy] copyRegFile(D:/ServerSync/www,trac/conf/trac.ini) -> (//debian12//home/www,trac.ini,/home/www/trac/conf,.unison.trac.ini.3cf645660f038354c49973b861281767.unison.tmp,modified on 2023-11-30 at 12:15:04  size 7449      unknown permissions)
[abort] Checking line 0
[server: pred] follow 'trac/conf/trac.ini' = false
[server: fspath] Os.findWorkingDir(/home/www,trac/conf/trac.ini) = (/home/www/trac/conf,trac.ini)
[server: copy] tryCopyMovedFile: -> .unison.trac.ini.3cf645660f038354c49973b861281767.unison.tmp /(86a468d364d8ac9b053abc05705cade5,)/
[server: xferhint] lookup: fp = (86a468d364d8ac9b053abc05705cade5,)
[server: copy] tryCopyMovedFile didn't work, so now we actually transfer
[server: copy] reallyTransferFile(D:/ServerSync/www,trac/conf/trac.ini) -> (/home/www/trac/conf,.unison.trac.ini.3cf645660f038354c49973b861281767.unison.tmp,trac.ini,modified on 2023-11-30 at 12:15:04  size 7449      unknown permissions)
[server: rsync] preprocessing
[server: rsynclog] block size = 700 bytes; block count = 10; strong checksum size = 3
[abort] Checking line 0
[rsync] compressing
[rsynclog] compression buffer size = 8192 bytes
[rsynclog] block size = 700 bytes
[rsynclog] 64 hash table entries
[rsynclog] 54 empty, 10 used, 0 collided
[rsynctoken] updating the compression buffer
[rsynctoken] new length = 7449 bytes
[rsynctoken] pushing string (pos:0/65500 len:702)
[rsynctoken] pushing block (pos:705/65500)
[rsynctoken] growing blocks (pos:710/65500)
[rsynctoken] pushing string (pos:710/65500 len:447)
[rsynctoken] pushing EOF (pos:1160/65500)
[rsynctoken] flushing the token queue
[rsynclog] hit-hit = 9, hit-miss = 0, miss-miss = 3, hit rate = 100%
[server: rsynclog] 10 blocks
[server: copy] Starting the actual transfer
[server: abort] Checking line 0
[server: rsynctoken] decompressing string (702 bytes)
[server: rsynctoken] decompressing 9 block(s) (sequence 1->9)
[server: rsynctoken] decompressing string (447 bytes)
[server: copy] transferResourceForkAndSetFileinfo .unison.trac.ini.3cf645660f038354c49973b861281767.unison.tmp
[server: copy] Resource fork transferred for trac.ini; doing last paranoid check
[server: xferhint] insertEntry: fspath=/home/www/trac/conf, path=.unison.trac.ini.3cf645660f038354c49973b861281767.unison.tmp, fp=(86a468d364d8ac9b053abc05705cade5,)
[files] rename(root=//debian12//home/www, localPath=trac/conf/trac.ini, pathOld=.unison.trac.ini.3cf645660f038354c49973b861281767.unison.tmp, pathNew=trac.ini)
[server: update] checkNoUpdates /home/www trac/conf/trac.ini
[server: update] buildUpdateRec: /home/www/trac/conf/trac.ini
[server: update] checkContentsChange: archStamp is inode (106173286) / info.inode (106173286) / times: 1701342849.592926 = 1701342849.592926... true / lengths: 7447 - 7447
[server: xferhint] insertEntry: fspath=/home/www, path=trac/conf/trac.ini, fp=(11c589c1b5293a98bf86827d1068c654,)
[server: update]   archive digest = (11c589c1b5293a98bf86827d1068c654,)   current digest = (11c589c1b5293a98bf86827d1068c654,)
[server: files] Renaming .unison.trac.ini.3cf645660f038354c49973b861281767.unison.tmp to trac.ini in /home/www/trac/conf; root is /home/www
[server: files] rename: moveFirst=false
[server: stasher] backup: /home/www / trac/conf/trac.ini
[server: pred] follow 'trac/conf/trac.ini' = false
[server: fspath] Os.findWorkingDir(/home/www,trac/conf/trac.ini) = (/home/www/trac/conf,trac.ini)
[server: pred] backup 'trac/conf/trac.ini' = false
[server: stasher] Path /home/www / trac/conf/trac.ini does not need to be backed up
[server: os] rename /home/www/trac/conf/.unison.trac.ini.3cf645660f038354c49973b861281767.unison.tmp to /home/www/trac/conf/trac.ini
[update] updateArchive D:/ServerSync/www trac/conf/trac.ini
[pred] ignore 'trac/conf/trac.ini' = false
[update] replaceArchiveLocal D:/ServerSync/www trac/conf/trac.ini
[update] Setting archive for //mywindows/D:/ServerSync/www
[pred] backupcurr 'trac/conf/trac.ini' = false
[END] Updating file trac/conf/trac.ini
<>[server: files] Contents of /home/www/trac/conf/trac.ini after renaming = 86a468d364d8ac9b053abc05705cade5
[server: pred] backupcurr 'trac/conf/trac.ini' = false
[server: xferhint] insertEntry: fspath=/home/www, path=trac/conf/trac.ini, fp=(86a468d364d8ac9b053abc05705cade5,)
[server: update] replaceArchiveLocal /home/www trac/conf/trac.ini
[server: update] Setting archive for //debian12//home/www
Unison 2.53.3 (ocaml 4.14.0) finished propagating changes at 12:17:50.77 on 30 Nov 2023, 0.202 s

问题原因分析 #

你的推测完全正确：

1. Windows没有Unix式的属主、用户组和权限体系，无法向Debian端传递这些元数据；
2. Unison同步时会在Debian端创建临时文件，该文件默认继承运行Unison的用户thomas的属主、组和权限；
3. 当前配置的owner=false/group=false是告诉Unison不尝试同步源端（Windows）的属主/组信息，而非保留目标端原有的属性；dontchmod=true和perms=0则禁止Unison修改文件权限，但临时文件创建时已经使用了用户默认权限，后续不会调整。

解决方法 #

1. 修改Unison配置，强制同步属性 #

若需要保持目标端文件属主为www-data，可调整配置如下：

owner = true
group = true
perms = -1
dontchmod = false
acl = false

• owner=true/group=true：Unison会尝试将目标文件的属主/组设置为源端对应值，但Windows无相关数据，因此需要在Debian端以拥有修改文件属主权限的用户（如root）运行Unison，或给thomas添加sudo权限并在同步时调用（注意安全风险）。

2. 同步后自动修正属性 #

若不想修改Unison运行用户，可在同步完成后执行脚本批量修正目标目录属性：

chown -R www-data:www-data /home/www/trac/conf/
chmod -R 660 /home/www/trac/conf/

可将该脚本与Unison同步命令合并为一个脚本，实现同步后自动修正。

3. 用rsync辅助同步（可选） #

如果Unison的权限处理不符合需求，可先用rsync从Windows同步到Debian并强制设置属性，再用Unison做双向同步补充：

rsync -avz --chown=www-data:www-data /mnt/windows-share/www/ /home/www/

跨系统同步局限性 #

Windows与Unix-like系统的文件元数据体系差异极大，Unison作为双向同步工具难以完美兼容两端属性。若需保证Unix端属性稳定，优先在Unix端控制同步后的属性修正，或搭配更侧重Unix元数据的同步工具。

内容的提问来源于stack exchange，提问作者Thomas853