---
name: "clsync"
section: "1"
platform: "linux"
package: "clsync"
version: "0.4.5-2.1+b2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/clsync"
---

# clsync(1)

live sync tool, written in GNU C

MONITOMONITORR.

## NAME

clsync - live sync tool, written in GNU C

## SYNOPSIS

**clsync \[ ... \] -- \[ sync-handler-arguments \]**

## DESCRIPTION

**clsync** executes *sync-handler* with appropriate arguments on FS events in directory *watch-dir* using the [**inotify**(7)](/inotify/7.md) or other FS monitoring subsystems.

## OPTIONS

This options can be passed as arguments or to be used in the configuration file.

To disable numeric option set to zero:

	\=0

To disable string option (for example path to file) set to empty string:

	\=

Also you can use previously set values while setting new options. Substring *%option\_name%* will be substituted with previously set value of option *option\_name*. (see  **CONFIGURATION FILE**)

*sync-handler-arguments* applies only to modes:

simple, direct, shell, rsyncdirect, rsyncshell

To set *sync-handler-arguments* in config file use '--'. An example:

\-- = -aH --exclude-from %EXCLUDE-LIST% --include-from=%INCLUDE-LIST% --exclude '\*' %watch-dir%/ %destination-dir%/

- **-W, --watch-dir** *watch-dir*

  Root directory to be monitored by **clsync**.

  Required.

- **-S, --sync-handler** *sync-handler*

  Path to *sync-handler* to be used for syncing by **clsync**. (see  *--mode*)

  Is required for all modes except "direct" and "rsyncdirect" \[see  **SYNC HANDLER MODES**\]

- **-R, --rules-file** *rules-file*

  Path to file with filter rules of objects to be monitored. (see  **RULES**)

  Is not set by default.

- **-D, --destination-dir** *destination-directory*

  Defines directory to sync to for modes "rsyncdirect", "rsyncso" and "so". (see *--mode*)

  Is not set by default.

- **-M, --mode** *mode*

  Sets syncing mode. Possible values:

  *simple*

  calls *sync-handler* for every event

  *direct*

  calls *sync-handler* for every sync with passing files lists as arguments

  *shell*

  calls *sync-handler* for every sync with passing files lists in a file

  *rsyncdirect*

  calls rsync by path *sync-handler* directly

  *rsyncshell*

  calls *sync-handler* that supposed to run rsync for every sync (recommended mode)"

  *rsyncso*

  loads shared object by path *sync-handler* with  [**dlopen**(3)](/dlopen/3.md) and calls function **clsyncapi\_rsync** function for every sync

  *so*

  loads shared object by path *sync-handler* with  [**dlopen**(3)](/dlopen/3.md) and calls function **clsyncapi\_sync** function for every sync

  See **SYNC HANDLER MODES**

  Required.

- **-b, --background**

  Daemonize, forcing clsync to fork() on start.

  Is not set by default.

- **-H, --config-file** *config-file-path*

  Use configuration from file *config-file-path* (see  **CONFIGURATION FILE**).

  Set to "/NULL/" if no config files should be read.

  Is not set by default.

- **-K, --config-block** *config-block-name*

  Use configuration block with name *config-block-name* (see  **CONFIGURATION FILE**).

  The default value is "default".

- **--config-block-inherits** *config-parent-block-name*

  Use configuration block with name *config-parent-block-name* as parent for *config-block-name* (see  **CONFIGURATION FILE**). Options from *config-parent-block-name* will be inherited to *config-block-name*.

  The default value is "default".

- **--custom-signals** *custom-signals*

  Set a list of signals and corresponding config block names. The config block will be use on catching the corresponding signal.

  Format is

  *signal:config-block-name\[,signal:config-block-name\[,...\]\]*

  For example:

  \--custom-signals=29:debug,28:normal

  In this line signals "28" and "29" will be added to the sighandler. And clsync will use options from config block "debug" on signal 29 and "normal" on signal 28.

  To reset all custom signals use the 0-th signal (e.g. "--custom-signals=0").

  The default value is "".

- **-z, --pid-file** *path-to-pidfile*

  Writes pid to file by path *path-to-pidfile*.

  Is not set by default.

- **--status-file** *status-file-path*

  Write status description into file with path *status-file-path*.

  Possible statuses:

  *starting*

  initializing subsystems and marking file tree with FS monitor subsystem

  *initsync*

  processing initial syncing

  *running*

  waiting for events or syncing

  *synchandler error*

  waiting between synchandler execution tries (after a failure) \[is used only while  **--threading**=off\]

  *rehashing*

  reloading configuration files

  *thread gc*

  running threads' garbage collector

  *preexit*

  executing the *--pre-exit-hook*

  *terminating*

  running the last iteration (if required) and preparing to die

  *exiting*

  executing the *--exit-hook* and cleaning up \[for [**valgrind**(1)](/valgrind/1.md)\]

  Is not set by default.

- **-r, --retries** *number-of-tries*

  Tries limit to sync with *sync-handler*.

  **clsync** will die after *number-of-tries* tries.

  To try infinite set "0".

  Delay between tries is equal to *--delay-sync* value.

  The default value is "1".

- **--ignore-failures**

  Don't die on sync failures.

  Is not set by default.

- **--exit-on-sync-skip**

  Exit if some event could be skipped due to any reason.

  For example FreeBSD has a very short BSM event queue (1024). So it may be overflowed and some events can not climb to the queue. This option forces **clsync** to exit if the queue had been overflowed.

  Is not set by default.

- **-p, --threading** *threading-mode*

  **\[Not available on Debian/kFreeBSD\]**

  Use [**pthreads**(7)](/pthreads/7.md) to parallelize syncing processes. For example if **clsync** (with **--threading=off**) is already syncing a huge file then all other syncs will be suspended until the huge file syncing finish. To prevent this suspends you can use "safe" or "full" threading mode.

  Possbile values:

  *off*

  disable threading for syncing processes.

  *safe*

  parallelize syncs but suspend syncings of object that are already syncing in another process (until the process finish).

  *full*

  parallelize syncs without suspendings.

  Characteristics:

  *off*

  New modifications won't be synced until old ones finish.

  *safe*

  Theoretically is the best way. But may utilize of lot of CPU if there's a lot of simultaneous parallel syncs. (also this way is not well tested)

  *full*

  May cause multiple simultaneous syncing of the same file, which in turn can cause bug inside *sync-handler* (see below).

  If you're running **clsync** with option **--threading=full** in conjunction with **rsync** with option **--backup**, you may catch a bug due to nonatomicity of rsync's file replace operation. (see **DIAGNOSTICS**)

  The default value is "off".

- **-Y, --output** *log-destination*

  Sets destination for log writing (errors, warnings, infos and debugging).

  Possible values:

  *stderr*\
   *stdout*\
   *syslog*

  The default value is "stderr".

- **--one-file-system**

  Don't follow to different devices' mount points. This option just adds option "FTS\_XDEV" for [**fts\_open**(3)](/fts_open/3.md) function.

  **Warning!** If you're using this option (but no --exclude-mount-points) **clsync** will write neither includes nor excludes of content of mount points.\
   This may cause problems e.g. you're using rsync for sync-handler without similar option "--one-file-system".

  Is not set by default.

- **-X, --exclude-mount-points**

  Forces *--one-file-system* but also add excludes to do not sync mount points.

  This requires to do [**stat**(2)](/stat/2.md) syscalls on every dir and can reduce performance.

  Is not set by default.

- **--socket** *socket-path*

  Create a control socket by path *socket-path*.

  This's very experimental feature.

  Is not set by default.

- **--socket-own** *socket-owner-user\[:socket-owner-group\]*

  Sets the control socket owner user (and group).

  Is not set by default

- **--socket-mod** *socket-mode*

  Sets the control socket mode \[see  [**chmod**(2)](/chmod/2.md)\].

  Is not set by default.

- **--standby-file** *standby-file-path*

  Sets file to path that should be checked before every sync. If file exists the sync will be suspended until the file is deleted. It may be useful if you need freeze destination directory while running some scripts.

  Is not set by default.

- **--max-iterations** *iterations-count*

  Sets synchronization iterations limit. One iteration means one sync-handler execution.

  *iterations-count*

  set to 0 means no limit (infinite loop).

  set to 1 means that only initial sync will be done

  set to n means that only initial sync and (n-1) sync-ups after that will be done

  Hint: This option may be useful in conjunction with --exit-on-no-events to prevent infinite sync-up processes.

  The default value is "0".

- **--modification-signature** *signature-mask*

  Sets file/dir modification recheck signature. If file is not modified (according to the signature) then don't sync it.

  See *struct stat* in [**lstat**(2)](/lstat/2.md) for possible fields.

  For example reasonable *signature-mask*-s can be "dev,ino,mode,uid,gid,rdev,size,atime,mtime,ctime" (there's an alias for that — "\*") or "uid,gid".

  Examples of use cases:

  **chown/chmod**

  If you're using clsync for fixing file/dir privileges \[using  [**chown**(1)](/chown/1.md) and/or [**chmod**(1)](/chmod/1.md)\] than reasonable signature will be "uid,gid".

  Full example: clsync -w5 -t5 -T5 -x1 -W /var/www/site.example.org/root -Mdirect -Schown --uid 0 --gid 0 -Ysyslog -b1 --modification-signature uid,gid -- --from=root www-data:www-data %INCLUDE-LIST%

  **bi-directional syncing**

  If you're going to setup bi-directional syncing then you may use --modification-signature "\*" to prevent sync loop between servers.

  **Not enough CPU**

  If rsync eats too many CPU with rechecking hashsums of files on their dry open()/close() due to some hacky script (for example "chown -R www-data:www-data" in cron) then you can use --modification-signature "dev,ino,mode,uid,gid,rdev,size,atime,mtime" (without "blksize", "blocks", "nlink" and "ctime").

  **Warning! This option may eat a lot of memory on huge file trees.**

  This option cannot be used together with "--cancel-syscalls=mon\_stat"

  To disable file/dir modification rechecking use empty value — "".

  The default value is "".

- **-k, --timeout-sync** *sync-timeout*

  Sets timeout for syncing processes. **clsync** will die if syncing process alive more than *sync-timeout* seconds.

  Set "0" to disable the timeout.

  The default value is "86400" \["24 hours"\].

- **-w, --delay-sync** *additional-delay*

  Sets the minimal delay (in seconds) between syncs.

  The default value is "30".

- **-t, --delay-collect** *ordinary-delay*

  Sets the delay (in seconds) to collect events about ordinary files and directories.

  The default value is "30".

- **-T, --delay-collect-bigfile** *bigfiles-delay*

  Sets the delay (in seconds) to collect events about "big files" (see *--threshold-bigfile*).

  The default value is "1800".

- **-B, --threshold-bigfile** *filesize-threshold*

  Sets file size threshold (in bytes) that separates ordinary files from "big files". Events about "big files" are processed in another queue with a separate collecting delay. This is supposed to be used as a means of unloading IO resources.

  To disable detection of "big files" set "0" (zero). This can improve performance by removing necessity in extra lstat() syscall.

  The default value is "134217728" \["128 MiB"\].

- **--cancel-syscalls** *syscalls-mask*

  Sets syscalls to be bypassed. This may be used for to squeeze more performance.

  Possible values:

  **mon\_stat**

  Skip lstat() calls while handling files/dirs events. This makes unpossible to determine files sizes (that is used by **--threshold-bigfile** option) and to use option **--modification-signature**.

  You can combine this values using commas.

  To disable this option just use empty value — "".

  The default value is "".

- **-L, --lists-dir** *tmpdir-path*

  Sets directory path to output temporary events-lists files.

  See **SYNC HANDLER MODES**.

  Is not set by default.

- **--have-recursive-sync**

  Use action "recursivesync" instead of "synclist" for directories that were just marked (see **SYNC HANDLER MODES** case **shell**).

  Is not set by default.

- **--synclist-simplify**

  Removes the first 3 parameters in list files of action "synclist" (see **SYNC HANDLER MODES** case **shell**).

  Is not set by default.

- **--rsync-inclimit** *rsync-includes-line-limit*

  Sets soft limit for lines count in files by path *rsync-listpath*. Unfortunately, rsync works very slowly with huge "--include-from" files. So, **clsync** splits that list with approximately *rsync-includes-line-limit* lines per list if it's too big, and executes by one rsync instance per list part. Use value "0" to disable the limit.

  The default value is "20000".

- **--rsync-prefer-include**

  Forces **clsync** to prefer a "lot of includes" method instead of a "excludes+includes" for rsync on recursive syncing.

  See cases **rsyncshell**, **rsyncdirect** and **rsyncso** of **SYNC HANDLER MODES**.

  This option is not recommended.

  Is not set by default.

- **-x, --ignore-exitcode** *exitcode*

  Forces **clsync** to do not process exitcode *exitcode* of *sync-handler* as an error. You can set multiple ignores by passing this option multiple times.

  Recommended values for rsync case is "24". You can set multiple values with listing a lot of "-x" options (e.g. "-x 23 -x 24") or via commas (e.g. "-x 23,24"). To drop the list use zero exitcode (e.g. "-x 0"). For example you can use "-x 0,23" to drop the list and set "23"-th exitcode to be ignored.

  Is not set by default (or equally is set to "0").

- **-U, --dont-unlink-lists**

  Do not delete list-files after *sync-handler* has finished.

  This may be used for debugging purposes.

  Is not set by default.

- **--fts-experimental-optimization**

  Enable experimental features to optimize file tree scanning while using [**fts**(3)](/fts/3.md). The features will be enabled by default after appropriate testing.

  At the moment the option doesn't do anything but can be used in future.

  Is not set by default.

- **-F, --full-initialsync**

  Ignore filter rules from *rules-file* on initial sync.

  This may be useful for quick start or e.g. if it's required to sync  "/var/log/" tree but not sync every change from there.

  Is not set by default.

- **--only-initialsync**

  Exit after initial syncing on clsync start.

  Is not set by default.

- **--exit-on-no-events**

  Exit if there's no events. Works like *--only-initialsync*, but also syncs events collected while the initial syncing.

  Unlike *--only-initialsync* this option uses FS monitor subsystem to monitor for new events while the initial syncing. This may reduce performance. On the other hand this way may be used to be sure, that everything is synced at the moment before clsync will exit.

  Is not set by default.

- **--skip-initialsync**

  Skip initial syncing on clsync start.

  Is not set by default.

- **--sync-on-quit**

  On SIGQUIT: clsync will perform one more final syncing to empty the queue of collected events before exit.

  Is not set by default.

- **--exit-hook** *path-of-exit-hook-program*

  Sets path of program to be executed on clsync exit.

  If this parameter is set then clsync will exec on exit:

  *path-of-exit-hook-program label*

  The execution will be skipped if initial sync wasn't complete.

  Is not set by default.

- **--pre-exit-hook** *path-of-pre-exit-hook-program*

  Sets path of program to be executed before the last sync iteration (see *--max-iterations*, *--exit-on-no-events* and  **SIGNALS**).

  If this parameter is set then clsync will exec on exit:

  *path-of-pre-exit-hook-program label*

  The execution will be skipped if initial sync wasn't complete.

  If **clsync** finishes due to *--exit-on-no-events* and *--pre-exit-hook* is set then the pre-exit hook will be executed and additional sync iteration will be triggered.

  Is not set by default.

- **-v, --verbose**

  This option is supposed to increase verbosity. But at the moment there's no "verbose output" in the code, so the option does nothing. :)

  Is not set by default.

- **-d, --debug**

  Increases debugging output. This may be supplied multiple times for more debugging information, up to a maximum of five "d" flags (more will do  nothing), for example "-d -d -d -d -d" or "-d5" (equivalent cases)

  Is not set by default.

- **--dump-dir**

  Directory to write clsync's instance information by signal 29 (see  **SIGNALS**). The directory shouldn't exists before dumping.

  Is set to "/tmp/clsync-dump-%label%" by default.

- **-q, --quiet**

  Suppresses error messages.

  Is not set by default.

- **--monitor** *monitor-subsystem*

  Switches FS monitor subsystem.

  Possible values:

  *inotify*

  [**inotify**(7)](/inotify/7.md) \[Linux, (FreeBSD via libinotify)\]

  Native, fast, reliable and well tested Linux FS monitor subsystem.

  There's no essential performance profit to use "inotify" instead of "kevent" on FreeBSD using "libinotify". It backends to "kevent" anyway.

  FreeBSD users: The libinotify on FreeBSD is still not ready and unusable for **clsync** to sync a lot of files and directories.

  *gio*

  Use **gio** library.

  Crossplatform and tested library that backends to kqueue on FreeBSD and inotify on Linux. See **inotify** and **kqueue** sections here for details.

  **Not well tested. Use with caution!**

  *kqueue*

  [**kqueue**(2)](/kqueue/2.md) \[FreeBSD, (Linux via libkqueue)\]

  A \*BSD kernel event notification mechanism (inc. timer, sockets, files etc).

  This monitor subsystem cannot determine file creation event, but it can determine a directory where something happened. So **clsync** is have to rescan whole dir every time on any content change. Moreover, kqueue requires an open() on every watched file/dir. But FreeBSD doesn't allow one to open() symlink itself (without following) and it's highly invasively to open() pipes and devices. So **clsync** just won't call open() on everything except regular files and directories. Consequently, **clsync** cannot determine if something changed in symlink/pipe/socket and so on. However it still can determine if it will be created or deleted by watching the parent directory and rescaning it on every appropriate event.

  Also this API requires to open every monitored file and directory. So it may produce a huge amount of file descriptors. Be sure that *kern.maxfiles* is big enough (in FreeBSD).

  CPU/HDD expensive way.

  **Not well tested. Use with caution!**

  Linux users: The libkqueue on Linux is not working. He-he :)

  *bsm*

  [**bsm**(3)](/bsm/3.md) \[FreeBSD\]

  Basic Security Module (BSM) Audit API.

  This is not a FS monitor subsystem, actually. It's just an API to access to  audit information (inc. logs). **clsync** can setup audit to watch FS events and report it into log. After that **clsync** will just parse the log via [**auditpipe**(4)](/auditpipe/4.md) \[FreeBSD\].

  Reliable, but hacky way. It requires global audit reconfiguration that may hopple audit analysis.

  **Warning!** FreeBSD has a limit for queued events. In default FreeBSD kernel it's only 1024 events. So choose **one** of:

  \- To patch the kernel to increase the limit.\
   \- Don't use **clsync** on systems with too many file events.\
   \- Use *bsm\_prefetch* mode (but there's no guarantee in this case anyway).

  See also option *--exit-on-sync-skip*.

  **Not well tested. Use with caution!** Also file /etc/security/audit\_control will be overwritten with:

  \#clsync\

  dir:/var/audit\
   flags:fc,fd,fw,fm,cl\
   minfree:0\
   naflags:fc,fd,fw,fm,cl\
   policy:cnt\
   filesz:1M

  unless it's already starts with "#clsync\\n" ("\\n" is a new line character).

  *bsm\_prefetch*

  The same as *bsm* but all BSM events will be prefetched by an additional thread to prevent BSM queue overflow. This may utilize a lot of memory on systems with a high FS events frequency.

  However the thread may be not fast enough to unload the kernel BSM queue. So it may overflow anyway.

  The default value on Linux is "inotify". The default value on FreeBSD is "kqueue".

- **-l, --label** *label*

  Sets a label for this instance of clsync. The *label* will be passed to *sync-handler* every execution.

  The default value is "nolabel".

- **-h, --help**

  Outputs options list and exits with exitcode "0".

  Is not set by default.

- **-V, --version**

  Outputs clsync version and exits with exitcode "0".

  Is not set by default.

- **--cgroup-group-name** *cg-group-name*

  Set cgroup group name \[see  **cgroup\_new\_cgroup**()\].

  Is set to "clsync/%PID%" by default.

## SECURITY OPTIONS

- **--secure-splitting**

  Implies "--splitting=process --check-execvp-arguments --seccomp-filter --forbid-devices"

- **-u, --uid** *uid*

  Drop user privileges to uid *uid* with [**setuid**(2)](/setuid/2.md)

  If there's a [**capabilities**(7)](/capabilities/7.md) support then the default value is "nobody" (or "65534" if "nobody" not found), otherwise the option is not set by default;

- **-g, --gid** *gid*

  Drop group privileges to gid *gid* with [**setgid**(2)](/setgid/2.md)

  If there's a [**capabilities**(7)](/capabilities/7.md) support then the default value is "nogroup" (or "65534" if "nogroup" not found), otherwise the option is not set by default;

- **--privileged-uid** *sync-handler-uid*

  An user ID to be used for the privileged process(see **--splitting=process**)**.**

  The default value is "$UID".

- **--privileged-gid** *sync-handler-gid*

  A group ID to be used for the privileged process(see **--splitting=process**)**.**

  The default value is "$GID".

- **--sync-handler-uid** *sync-handler-uid*

  An user ID to be used for *sync-handler*.

  See **--preserve-capabilities**.

  The default value is same as for  **--privileged-uid**.

- **--sync-handler-gid** *sync-handler-gid*

  A group ID to be used for *sync-handler*.

  See **--preserve-capabilities**.

  The default value is same as for  **--privileged-gid**.

- **-C, --preserve-capabilities** *capabilities-list*

  **\[Linux only, requires capabilities\]**

  Use [**capset**(2)](/capset/2.md) and [**prctl**(2)](/prctl/2.md) to preserve "CAP\_DAC\_READ\_SEARCH", "CAP\_SETUID" or/and "CAP\_SETGID" \[see  [**capabilities**(7)](/capabilities/7.md)\] Linux capability for process using [**fts**(3)](/fts/3.md), [**inotify**(7)](/inotify/7.md) and [**execve**(2)](/execve/2.md). This allows the preservation of enough FS privileges to watch a file tree and execute the *sync-handler* with required uid and gid \[see  **--sync-handler-uid** and **--sync-handler-gid**\] after dropping privileges via [**setuid**(2)](/setuid/2.md) and [**setgid**(2)](/setgid/2.md) \[see **--uid** and **--gid**\]

  Possible values:

  **CAP\_DAC\_READ\_SEARCH**

  To bypass FS read checks (for **fts** and **inotify**).

  **CAP\_SETUID**

  To be able to use [**setuid**(2)](/setuid/2.md) before [**execve**(2)](/execve/2.md) on the **sync-handler**.

  **CAP\_SETGID**

  To be able to use [**setgid**(2)](/setgid/2.md) before [**execve**(2)](/execve/2.md) on the **sync-handler**.

  **CAP\_KILL**

  To be able to kill setuid()-ed processes

  Any combinations of this values are also supported. The list may be presented as a comma separated values, like:

  CAP\_DAC\_READ\_SEARCH,CAP\_SETUID,CAP\_SETGID

  The default value is "CAP\_DAC\_READ\_SEARCH,CAP\_SETUID,CAP\_SETGID,CAP\_KILL" if the **clsync** runner have such privileges.

- **--inherit-capabilities**

  **\[Linux only, requires capabilities\]**

  Sets a mode for capabilities inheriting.

  Possible values:

  **permitted**

  Inherits all permitted capabilities

  **dont-touch**

  Don't change inheritable capabilities set

  **clsync**

  Use **clsync**'s effective capabilities set

  **empty**

  Reset all capabilities

  The default value is "empty".

- **--splitting** *splitting-type*

  Split the process/thread to privileged and non-privileged. This's an additional way to secure your system from any bug in **clsync** while running it with capabilities or root privileges. But **clsync** may utilize in few times more CPU resources. So it's a performance vs security trade off.

  You can essentialy reduce the overhead with using "high load locks" ("--enable-highload-locks" of "./configure" file).

  If you're using this option and running the *sync-handler* with the root user then it's highly recommended to enable **--check-execvp-arguments**, too. Otherwise in case of **clsync** security bug a hacker will be able to use execvp() with any arguments with root privileges.

  Possible values:

  **off**

  Disable this feature

  **thread**

  **\[Linux only, requires capabilities\]**

  Creates a separate thread for privileged operations.

  It's highly recommended to enable **--seccomp-filter** in this case. But that will forbid **--threading**.

  **process**

  More secure and portable way, but uses separate process and:

  \- forbids fanotify (that is not implemented yet anyway);\
   \- more complex code (and higher probability of error).\
   \- slower due to copying data between private and shared memory pages.

  **Recommended.**

  Is set to "off" by default.

- **--check-execvp-arguments**

  **\[Requires --splitting=\[thread\|process\]\]**\
   **\[Blocks --mode=direct\]**

  Enables execvp() arguments recheck in the privileged process (in case of their substitution to any exploit-given arguments).

  This option doesn't utilize a lot of CPU resources but forbids run-time changing of *sync-handler-arguments* and hook file paths.

  This option cannot be used in conjunction with **--mode**=direct due to an arbitrary number of arguments in this mode.

  Is not set by default.

- **--add-permitted-hook-files** *\[hook-path0,\[hook-path1\[,...\]\]\]*

  **\[Requires --check-execvp-arguments\]**

  Adds paths to the list of permitted hook paths to bypass **--check-execvp-arguments** checks. It may be required if you're going to change the hooks in run-time using **--custom-signals** or **--socket**.

  Is not set by default.

- **--seccomp-filter**

  **\[Linux only\]**

  Use **seccomp** filter to forbid syscalls that shouldn't be used by clsync.

  Forbid all syscalls for non-privileged process/thread, but

  futex inotify\_init1 alert stat fstat lstat open write close wait4 unlink tgkill clock\_gettime rt\_sigreturn brk mmap munmap wait4 rmdir exit\_group select read rt\_sigprocmask rt\_sigaction nanosleep

  Is not set by default.

- **--permit-mprotect**

  **\[Requires --seccomp-filter\]**

  Permits [**mprotect**(2)](/mprotect/2.md) syscall.

  This syscall is required by [**pthread\_create**(3)](/pthread_create/3.md), so it's required for **--threading**.

  Makes --shm-mprotect to be useless.

  Also it enables ability to change memory of privileged thread from non-privileged, so using of **--splitting=thread** with this option is useless, too.

  Is set to "0" by default if --splitting is set. Otherwise "1".

- **--shm-mprotect**

  **\[Requires --splitting=process\]**

  Forbid writing or reading to/from shared memory when it shouldn't be. [**mprotect**(2)](/mprotect/2.md) is used for the protection.

  This option is useless while **--permit-mprotect** is enabled.

- **--chroot** *chroot-directory*

  clsync chroot()-s \[see [**chroot**(2)](/chroot/2.md)\] to directory *chroot-directory* before any syncing processes.

  This option may be used in conjunction with **--uid**, **--gid** or/and **--pivot-root** for security reasons.

  Remember! If you're chroot()-ing somewhere, the *sync-handler* will be limited by the chroot-environment, too. If you're using rsync then you may want to "mount --bind" some directories to the *chroot-directory*.

  Is not set by default.

- **--pivot-root** *pivot-root-way*

  **\[Linux only, requires --chroot\]**

  Sets a way of using [**pivot\_root**(2)](/pivot_root/2.md) syscall to the *chroot-directory* (to [**umount**(2)](/umount/2.md) old rootfs).

  Possible values:

  **auto**

  Creates a directory "/dev/shm/clsync-rootfs", [**unshare**(2)](/unshare/2.md)-ing the mount namespace, [**mount**(2)](/mount/2.md)-s the *chroot-directory* to the directory and then [**pivot\_root**(2)](/pivot_root/2.md)-ing, [**chroot**(2)](/chroot/2.md)-ing and [**umount**(2)](/umount/2.md)-ing old rootfs. Directory "/dev/shm/clsync-rootfs" won't be deleted after **clsync** finish.

  **auto-ro**

  The same as **auto** but mounts the directory with read-only option (MS\_RDONLY).

  **direct**

  [**unshare**(2)](/unshare/2.md)-ing the mount namespace, [**pivot\_root**(2)](/pivot_root/2.md)-ing, [**chroot**(2)](/chroot/2.md)-ing and [**umount**(2)](/umount/2.md)-ing old rootfs. Directory "old\_root" should be created in *chroot-directory* before running **clsync** in this mode.

  **off**

  Don't [**pivot\_root**(2)](/pivot_root/2.md).

  The default value is "off". If **--chroot** is used then recommended value is "auto-ro".

- **--mountpoints** *\[mountpoint\[,mountpoint\[,mountpoint\]\]\]*

  **\[Linux only\]**

  Umount (with MNT\_DETACH) everything except listed mountpoints.

  Supposed to be used for security reasons as an alternative to **--pivot-root** option.

  Is not set by default.

- **--detach-network** *detach-network-mode*

  **\[Linux only\]**

  Removes network in **clsync** instance.

  Possible values:

  **everywhere**

  Removes network for all processes.

  **non-privileged**

  Removes network from non-privileged process if option **--process-splitting** is enabled, otherwise doesn't do anything.

  **off**

  Don't do anything.

  The default value is "non-privileged".

- **--detach-ipc**

  **\[Linux only\]**

  Make an own IPC namespace.

  Is set by default.

- **--detach-miscellanea**

  **\[Linux only\]**

  [**unshare**(2)](/unshare/2.md) on everything not listed above.

  Is not set by default.

- **--forbid-devices**

  **\[Linux only\]**

  Forbid any access to all devices except listed ones:

  read access to:

  /dev/console\
   /dev/zero\
   /dev/urandom\
   /dev/random

  write access to:

  /dev/console\
   /dev/null

  Is not set by default.

## PERFORMANCE

Recommendations to improve the performance:

\- Disable thread/process splitting.\
 \- Don't use clsync rules (use rules on sync-handler side) or/and use option "--full-initialsync"\
 \- Use option "-B0".\
 \- Use option "--cancel-syscalls=mon\_stat".\
 \- Use option "-p safe" or "-p full".\
 \- Disable debugging with "-d0" or better disable debugging support at all with "./configure" option "--enable-debug=no"\
 \- Don't use option "--exclude-mount-points"\
 \- Free memory for disk cache\

You shouldn't follow all this recommendation blindfold. You should use only the ideas that fixes performance problems in your specific use case. And only if it's necessary.

## SYNC HANDLER MODES

**clsync** executes *sync-handler* that supposed to take care of the actual syncing process. Therefore **clsync** is only a convenient way to run a syncing script.

**clsync** can run *sync-handler* in seven ways. Which way will be used depends on specified mode (see *--mode*)

*sync-handler-arguments* are used only in modes:

simple\
 direct\
 shell\
 rsyncdirect\
 rsyncshell

If *sync-handler-arguments* are not set then the default setting is used (see below).

case **simple**

Executes for every syncing file/dir:

*sync-handler sync-handler-arguments*

Default *sync-handler-arguments* are:

sync *%label% %EVENT-MASK% %INCLUDE-LIST%*

In this case, *sync-handler* is supposed to non-recursively sync file or directory by path *%INCLUDE-LIST%*. With *%EVENT-MASK%* it's passed bitmask of events with the file or directory (see  "/usr/include/linux/inotify.h").

Additional substitutions:

**%EVENT-MASK%**

Is replaced by integer of events IDs.

**%INCLUDE-LIST%**

Is replaced by absolute path of a file/dir to be synced.

case **direct**

Executes for every sync:

*sync-handler sync-handler-arguments*

Default *sync-handler-arguments* are:

%INCLUDE-LIST% %destination-dir%/

Additional substitutions:

**%INCLUDE-LIST%**

Is replaced by a list of relative paths of files/dirs to be synced.

case **shell**

Executes for every sync (if  **recursivesync** is not used instead):

*sync-handler sync-handler-arguments*

Default *sync-handler-arguments* are:

synclist %label% %INCLUDE-LIST-PATH%

Default *sync-handler-arguments* for initial sync if *--have-recursive-sync* is set are:

initialsync %label% %INCLUDE-LIST%

In this case, *sync-handler* is supposed to non-recursively sync files and directories from list in a file by path %INCLUDE-LIST-PATH% on "synclist".

Also *sync-handler* is supposed to recursively sync data from directory by path %INCLUDE-LIST-PATH% with manual excluding extra files on "initialsync".

Additional substitutions:

**%TYPE%**

Is replaced by "sync"/"initialsync".

**%INCLUDE-LIST-PATH%**

Is replaced by the path of the include list file.

**%INCLUDE-LIST%**

Is replaced by a list of relative paths of files/dirs to be synced.

Not recommended. Not well tested.

case **rsyncdirect**

Executes for every sync:

*sync-handler sync-handler-arguments*

*sync-handler* is supposed to be a path to **rsync** binary.

Default *sync-handler-arguments* are:

\-aH --delete --exclude-from %EXCLUDE-LIST-PATH% --include-from %INCLUDE-LIST-PATH% --exclude='\*' %watch-dir%/ %destination-dir%/

if option *--rsync--prefer-include* is not set and

\-aH --delete --include-from %INCLUDE-LIST-PATH% --exclude='\*' %watch-dir%/ %destination-dir%/

if the option is set

Error code "24" from *sync-handler* will be ignored in this case. We also recommend to ignore exitcode "23".

Additional substitutions:

**%INCLUDE-LIST-PATH%**

Is replaced by the path of the include list file

**%EXCLUDE-LIST-PATH%**

Is replaced by the path of the exclude list file

**%RSYNC-ARGS%**

Is replaced by default *sync-handler-arguments*, but without "%watch-dir%/ %destination-dir%/"

Recommended case.

case **rsyncshell**

Executes for every sync:

*sync-handler sync-handler-arguments*

Default *sync-handler-arguments* are:

rsynclist %label% %INCLUDE-LIST-PATH% \[%EXCLUDE-LIST-PATH%\]

In this case, *sync-handler* is supposed to run "rsync" application with parameters:

\-aH --delete-before --include-from *%INCLUDE-LIST-PATH%* --exclude '\*'

if option *--rsync-prefer-include* is enabled.

And with parameters:

\-aH --delete-before --exclude-from *%EXCLUDE-LIST-PATH%* --include-from *%INCLUDE-LIST-PATH%* --exclude '\*'

if option *--rsync-prefer-include* is disabled.

Additional substitutions:

**%INCLUDE-LIST-PATH%**

Is replaced by the path of the rsync include list file

**%EXCLUDE-LIST-PATH%**

Is replaced by the path of the rsync exclude list file

Recommended case.

case **rsyncso**

In this case there's no direct exec\*() calling. In this case **clsync** loads *sync-handler* as a shared library with [**dlopen**(3)](/dlopen/3.md) and calls function "int clsyncapi\_rsync(const char \*inclist, const char \*exclist)" from it for every sync.\
 **inclist** is a path to file with rules for "--include-from" option of rsync. This argument is always not NULL.\
 **exclist** is a path to file with rules for "--exclude-from" option of rsync. This argument is NULL if **--rsync-prefer-include** is set.\
 *Excludes takes precedence over includes.*

Also may be defined functions "int clsyncapi\_init(ctx\_t \*, indexes\_t \*)" and "int clsyncapi\_deinit()" to initialize and deinitialize the syncing process by this shared object.

To fork the process should be used function "pid\_t clsyncapi\_fork(ctx\_t \*)" instead of "pid\_t fork()" to make clsync be able to kill the child.

See example file "clsync-synchandler-rsyncso.c".

Recommended case.

case **so**

In this case there's no direct exec\*() calling. In this case **clsync** loads *sync-handler* as a shared library with [**dlopen**(3)](/dlopen/3.md) and calls function "int clsyncapi\_sync(int n, api\_eventinfo\_t \*ei)" from it for every sync. **n** is number of elements of **ei**. **ei** is an array of structures with information about what and how to sync (see below).

api\_eventinfo\_t is a structure:

struct api\_eventinfo {\
\
         uint32\_t         evmask;		// event bitmask for file/dir by path **path**.\
\
         uint32\_t         flags;		// flags of "how to sync" the file/dir\
\
         size\_t           path\_len;		// strlen(path)\
\
         const char      \*path;		// the **path** to file/dir need to be synced\
\
         eventobjtype\_t   objtype\_old;	// type of object by path **path** before the event.\
\
         eventobjtype\_t   objtype\_new;	// type of object by path **path** after the event.\
 };\
 typedef struct api\_eventinfo api\_eventinfo\_t;

The event bitmask (evmask) values can be learned from "/usr/include/linux/inotify.h".

There may be next flags' values (flags):

enum eventinfo\_flags {\
\
         EVIF\_NONE        = 0x00000000,	// No modifier\
\
         EVIF\_RECURSIVELY = 0x00000001	// sync the file/dir recursively\
 };

Flag "EVIF\_RECURSIVELY" may be used if option *--have-recursive-sync* is set.

Is that a file or directory by path **path** can be determined with **objtype\_old** and **objtype\_new**.\
 **objtype\_old** reports about which type was the object by the path before the event.\
 **objtype\_new** reports about which type became the object by the path after the event.

**objtype\_old** and **objtype\_new** have type **eventobjtype\_t**.

enum eventobjtype {\
\
         EOT\_UNKNOWN     = 0,	// Unknown\
\
         EOT\_DOESNTEXIST = 1,	// Doesn't exist (not created yet or already deleted)\
\
         EOT\_FILE        = 2,	// File\
\
         EOT\_DIR         = 3,	// Directory\
 } typedef enum eventobjtype eventobjtype\_t;

Also may be defined functions "int clsyncapi\_init(options\_t \*, indexes\_t \*)" and "int clsyncapi\_deinit()" to initialize and deinitialize the syncing process by this shared object.

To fork the process should be used function "pid\_t clsyncapi\_fork(options\_t \*)" instead of "pid\_t fork()" to make clsync be able to kill the child.

See example file "clsync-synchandler-so.c".

Recommended case.

## ENVIRONMENT VARIABLES

Recognized variables - variables used by clsync.

**Recognized variables**

HOME - user's HOME directory, clsync looks for configuration file here

TMPDIR - use this directory as a prefix to create clsync temporary directory inside, if unset */tmp* will be used

Output variables - variables that are set by clsync before calling *sync-handler*.

**Output variables**

CLSYNC\_STATUS -  **clsync**'s status (see possible statuses in description of *--status-file*)

CLSYNC\_ITERATION - count of done synchronizaton iterations after initial sync see --max-iterations option

## RULES

Filter rules can be used to set which events clsync should monitor and which events it should ignore.

**Caution!** This rules doesn't guarantee that filtered file/dir won't be synced. This can occur because file or directory can appear in the moment of **sync-handler** running (or after it but before the  **sync-handler** will reach the directory), so it'll be too late to add an exclusion. If you need a guarantee of file syncing preventing you can use internal filter rules of the **sync-handler** program (for example, rsync has options "--exclude", "--exclude-from" and "--filter") or use disable any "recursive" syncs in **clsync** (and remove "-av" option of rsync if it's used). To disable recursive syncs you can use:

**simple**

Already non-recursive

**direct**

Already non-recursive

**shell**

Don't enable option --have-recursive-sync.

**rsyncdirect**

Use option --rsync-prefer-include and set *sync-handler-arguments* to -lptgoD --delete --include-from %INCLUDE-LIST-PATH% --exclude='\*' %watch-dir%/ %destination-dir%/

**rsyncshell**

Use option --rsync-prefer-include.

**rsyncso**

Use option --rsync-prefer-include.

**so**

Don't enable option --have-recursive-sync.

Filter rules can be placed into *rules-file* with one rule per line.

Rule format: *\[+-\]\[fdWwms\*\]regexp*

*+* - means include;\
 *-* - means exclude;\
 *f* - means file;\
 *d* - means directory (the same as an combination of "w" + "m" + "s");\
 *w* - means walking to directory;\
 *m* - means monitor events in the directory;\
 *s* - means sync the the directory if modified;\
 *W* - means walk + monitor the directory (the same as an combination of "w" + "m");\
 *\** - means all.

For example: -\*^/\[Tt\]est

It's not recommended to use *w* rules in modes "rsyncdirect", "rsyncshell" and "rsyncso". [**rsync**(1)](/rsync/1.md) allows one to set syncing and walking only together in "--include" rules ("--files-from" is not appropriate due to problem with syncing files deletions). So there may be problems with clsync's *w* rules in this cases.

More examples:

Syncing pwdb files and sshd\_config (non-rsync case):

	\# which files to sync:\
\
 	\+f^passwd$\
\
 	\+f^group$\
\
 	\+f^shadow$\
\
 	\+f^ssh/sshd\_config$\

	\# walk and monitor next directories:\
\
 	\+W^$\
\
 	\+W^ssh$\

	\# forbid the rest:\
\
 	\-\*

Syncing pwdb files and sshd\_config (rsync case):

	\+f^passwd$\
\
 	\+f^group$\
\
 	\+f^shadow$\
\
 	\+f^ssh/sshd\_config$\
\
 	\+d^$\
\
 	\+d^ssh$\
\
 	\-\*

Syncing /srv/lxc tree (rsync case):

	\-d/sess(ion)?s?$\
\
 	\-f/tmp/\
\
 	\+\*

## SIGNALS

1  - (HUP) rereads filter rules

2  - (INT) exits without waiting of syncing processes ("hard kill", kills children)

3  - (QUIT) waits for current syncing processes and exit ("soft kill", waits for children). See also *--sync-on-quit*.

10 - runs threads' GC function

12 - runs full resync

15 - (TERM) exits without waiting of syncing processes ("hard kill", kills children)

16 - interrupts sleep()/select() and wait() \[for debugging and internal uses\]

29 - dump information to *dump-dir* \[for debugging\]

If you need to kill clsync but leave children then you can use 9-th (KILL) signal.

## DIAGNOSTICS

**clsync** misses events:

Try to run command: sysctl fs.inotify.max\_queued\_events=1048576

Initial rsync process works very slow on clsync start

Probably there's too huge exclude list is passed to rsync. This can happened if you're excluding with regex in clsync's rules a lot of thousands files. They will be passed to rsync's exclude list one by one.

To diagnose it, you can use "-U" option and look into  *rsync-exclude-listpath* file (see **SYNC HANDLER** case  **d**)

To prevent this, it's recommended to write such rules for rsync directly  (not via clsync).

For example, often problem is with PHP's session files. You shouldn't exclude them in clsync's rules with "-f/sess\_.\*", but you should exclude it in rsync directly (e.g with «--exclude "sess\_\*"»).

The following diagnostics may be issued on stderr:

Error: Cannot inotify\_add\_watch() on \[...\]: No space left on device (errno: 28)

Not enough inotify watching descriptors is allowed. It can be fixed by increasing value of "sysctl fs.inotify.max\_user\_watches"

Error: Got non-zero exitcode *exitcode* \[...\]

*sync-handler* returned non-zero exitcode. Probably, you should process exitcodes in it or your syncer process didn't worked well. I case of using rsync, you can find the exitcodes meanings in **man 1 rsync**.

If *exitcode* equals to 23 and you're using **clsync** in conjunction with **rsync**, this may happen, for example, in the following cases:

\- Not enough space on destination.

\- You're running clsync with  **--threading=full** and rsync with **--backup**. See a bugreport ⟨URL: https://bugzilla.samba.org/show\_bug.cgi?id=10081 ⟩.

To confirm the problem, you can try to add "return 0" or "exit 0" into your *sync-handler*.

**Bad system call**

If --use-seccomp option is enabled then the error is probably caused by using of forbidden syscall. It's a **clsync** bug or hack attack attempt.

To get support see **SUPPORT**.

## CONFIGURATION FILE

**clsync** supports configuration file.

By default **clsync** tries to read next files (in specified order):

\~/.clsync.conf\
 /etc/clsync/clsync.conf

This may be overridden with option *--config-file*.

**clsync** reads only one configuration file. In other words, if option *--config-file* is not set and file **~/.clsync.conf** is accessible and parsable, **clsync** will not try to open **/etc/clsync/clsync.conf**. Command line options have precedence over config file options.

Configuration file is parsed with glib's g\_key\_file\_\* API. That means, that config should consits from groups (blocks) of key-value lines as in the example:

\[default\]\
 background = 1\
 mode = rsyncshell\
 debug = 0\
 output = syslog\
 label = default\
 pid-file = /var/run/clsync-%label%.pid

\[debug\]\
 config-block-inherits = default\
 debug = 5\
 background = 0\
 output = stderr

\[test\]\
 mode=rsyncdirect\
 debug=3

Also glib's **gkf** API doesn't support multiple assignments. If you need to list some values (e.g. exitcodes) just list them with commas in single assignment (e.g. "ignore-exitcode=23,24").

In this example there're 3 blocks are set - "default", "debug" and "test". And block "debug" inherited setup of block "default" except options "debug", "background" and "output".

By default **clsync** uses block with name "default". Block name can be set by option *--config-block*.

## CLUSTERING

Not implemented yet. **Don't try to use cluster functionality.**

Not described yet.

## EXAMPLES

**Mirroring a directory:**

clsync -Mrsyncdirect -W/path/to/source\_dir -D/path/to/destination\_dir

**Syncing 'authorized\_keys' files:**

mkdir -p /etc/clsync/rules\
 printf "+w^$\\n+w^\[^/\]+$\\n+W^\[^/\]+/.ssh$\\n+f^\[^/\]+/.ssh/authorized\_keys$\\n-\*" \> /etc/clsync/rules/authorized\_files\_only\
 clsync -Mdirect -Scp -W/mnt/master/home/ -D/home -R/etc/clsync/rules/authorized\_files\_only -- -Pfp --parents %INCLUDE-LIST% %destination-dir%

**Mirroring a directory, but faster:**

clsync -w5 -t5 -T5 -Mrsyncdirect -W/path/to/source\_dir -D/path/to/destination\_dir

**Instant mirroring of a directory:**

clsync -w0 -t0 -T0 -Mrsyncdirect -W/path/to/source\_dir -D/path/to/destination\_dir

**Making two directories synchronous:**

clsync -Mrsyncdirect --background -z /var/run/clsync0.pid --output syslog -Mrsyncdirect -W/path/to/dir1 -D/path/to/dir2 --modification-signature '\*'\
 clsync -Mrsyncdirect --background -z /var/run/clsync1.pid --output syslog -Mrsyncdirect -W/path/to/dir2 -D/path/to/dir1 --modification-signature '\*'

**Fixing privileges of a web-site:**

clsync -w3 -t3 -T3 -x1 -W/var/www/site.example.org/root -Mdirect -Schown --uid 0 --gid 0 -Ysyslog -b1 --modification-signature uid,gid -- --from=root www-data:www-data %INCLUDE-LIST%

**'Atomic' sync:**

clsync --exit-on-no-events --max-iterations=20 --mode=rsyncdirect -W/var/www\_new -Srsync -- %RSYNC-ARGS% /var/www\_new/ /var/www/

**Moving a web-server:**

clsync --exit-on-no-events --max-iterations=20 --pre-exit-hook=/root/stop-here.sh --exit-hook=/root/start-there.sh --mode=rsyncdirect --ignore-exitcode=23,24 --retries=3 -W /var/www -S rsync -- %RSYNC-ARGS% /var/www/ rsync://clsync@another-host/var/www/

**Copying files to slave-nodes using** [**pdcp**(1)](/pdcp/1.md):

clsync -Msimple -S pdcp -W /opt/global -b -Y syslog -- -a %INCLUDE-LIST% %INCLUDE-LIST%

**Copying files to slave-nodes using** [**uftp**(1)](/uftp/1.md):

clsync -Mdirect -S uftp -W/opt/global --background=1 --output=syslog -- -M 248.225.233.1 %INCLUDE-LIST%

**A dry running to see** [**rsync**(1)](/rsync/1.md) **arguments that clsync will use:**

clsync -Mrsyncdirect -S echo -W/path/to/source\_dir -D/path/to/destination\_dir

**An another dry running to look how clsync will call** [**pdcp**(1)](/pdcp/1.md):

clsync -Msimple -S echo -W /opt/global -b0 -- pdcp -a %INCLUDE-LIST% %INCLUDE-LIST%

**Automatically run 'make build' if any '\*.c' file changed**

printf "%s\\n" "+f.c$" "-f" \| clsync --have-recursive-sync -W . -R /dev/stdin -Mdirect -r1 --ignore-failures -t1 -w1 -Smake -- build

More working examples you can try out in "/usr/share/doc/clsync/examples/" directory. Copy this directory somewhere (e.g. into "/tmp"). And try to run "clsync-start-rsync.sh" in there. Any files/directories modifications in "testdir/from" will be synced to "testdir/to" in a few seconds.

## AUTHOR

Dmitry Yu Okunev \<dyokunev@ut.mephi.ru\> 0x8E30679C

## SUPPORT

You can get support on official IRC-channel in Freenode "#clsync" or on github's issue tracking system of the clsync repository ⟨URL: https://github.com/clsync/clsync ⟩.

Don't be afraid to ask about clsync configuration, ;).

## SEE ALSO

[**rsync**(1)](/rsync/1.md), [**pthreads**(7)](/pthreads/7.md), [**inotify**(7)](/inotify/7.md) [**kqueue**(2)](/kqueue/2.md)