2.1. Syncthing

2.1.1. Synopsis

syncthing [-audit] [-auditfile=<file|-|-->] [-browser-only] [device-id]
          [-generate=<dir>] [-gui-address=<address>] [-gui-apikey=<key>]
          [-home=<dir>] [-logfile=<filename>] [-logflags=<flags>]
          [-no-browser] [-no-console] [-no-restart] [-paths] [-paused]
          [-reset-database] [-reset-deltas] [-unpaused] [-upgrade]
          [-upgrade-check] [-upgrade-to=<url>] [-verbose] [-version]

2.1.2. Description

Syncthing lets you synchronize your files bidirectionally across multiple devices. This means the creation, modification or deletion of files on one machine will automatically be replicated to your other devices. We believe your data is your data alone and you deserve to choose where it is stored. Therefore Syncthing does not upload your data to the cloud but exchanges your data across your machines as soon as they are online at the same time.

2.1.3. Options

-audit

Write events to timestamped file audit-YYYYMMDD-HHMMSS.log.

-auditfile=<file|-|-->

Use specified file or stream ("-" for stdout, "--" for stderr) for audit events, rather than the timestamped default file name.

-browser-only

Open the web UI in a browser for an already running Syncthing instance.

-device-id

Print device ID to command line.

-generate=<dir>

Generate key and config in specified dir, then exit.

-gui-address=<address>

Override GUI listen address.

-home=<dir>

Set configuration directory. The default configuration directory is $HOME/.config/syncthing (Unix-like), $HOME/Library/Application Support/Syncthing (Mac) and %LOCALAPPDATA%\Syncthing (Windows).

-logfile=<filename>

Set destination filename for logging (use "-" for stdout, which is the default option).

-logflags=<flags>

Select information in log line prefix. The -logflags value is a sum of the following:

  • 1: Date
  • 2: Time
  • 4: Microsecond time
  • 8: Long filename
  • 16: Short filename

To prefix each log line with date and time, set -logflags=3 (1 + 2 from above). The value 0 is used to disable all of the above. The default is to show time only (2).

-no-browser

Do not start a browser.

-no-console

Hide the console window. (On Windows only)

-no-restart

Disable the Syncthing monitor process which handles restarts for some configuration changes, upgrades, crashes and also log file writing (stdout is still written).

-paths

Print the paths used for configuration, keys, database, GUI overrides, default sync folder and the log file.

-paused

Start with all devices and folders paused.

-reset-database

Reset the database, forcing a full rescan and resync. Create .stfolder folders in each sync folder if they do not already exist. Caution: Ensure that all sync folders which are mountpoints are already mounted. Inconsistent versions may result if the mountpoint is later mounted and contains older versions.

-reset-deltas

Reset delta index IDs, forcing a full index exchange.

-unpaused

Start with all devices and folders unpaused.

-upgrade

Perform upgrade.

-upgrade-check

Check for available upgrade.

-upgrade-to=<url>

Force upgrade directly from specified URL.

-verbose

Print verbose log output.

-version

Show version.

2.1.4. Exit Codes

0
Success / Shutdown
1
Error
2
Upgrade not available
3
Restarting
4
Upgrading

Some of these exit codes are only returned when running without a monitor process (with environment variable STNORESTART set). Exit codes over 125 are usually returned by the shell/binary loader/default signal handler. Exit codes over 128+N on Unix usually represent the signal which caused the process to exit. For example, 128 + 9 (SIGKILL) = 137.

2.1.5. Proxies

Syncthing can use a SOCKS, HTTP, or HTTPS proxy to talk to the outside world. The proxy is used for outgoing connections only - it is not possible to accept incoming connections through the proxy. The proxy is configured through the environment variable all_proxy. Somewhat unusually, this variable must be named in lower case - it is not “ALL_PROXY”. For example:

$ export all_proxy=socks://192.0.2.42:8081

2.1.6. Development Settings

The following environment variables modify Syncthing’s behavior in ways that are mostly useful for developers. Use with care. If you start Syncthing from within service managers like systemd or supervisor, path expansion may not be supported.

STTRACE

Used to increase the debugging verbosity in specific or all facilities, generally mapping to a Go package. Enabling any of these also enables microsecond timestamps, file names plus line numbers. Enter a comma-separated string of facilities to trace. syncthing -help always outputs an up-to-date list. The valid facility strings are:

Main and operational facilities:
config
Configuration loading and saving.
db
The database layer.
main
Main package.
model
The root hub; the largest chunk of the system. File pulling, index transmission and requests for chunks.
scanner
File change detection and hashing.
versioner
File versioning.
Networking facilities:
beacon
Multicast and broadcast UDP discovery packets: Selected interfaces and addresses.
connections
Connection handling.
dialer
Dialing connections.
discover
Remote device discovery requests, replies and registration of devices.
nat
NAT discovery and port mapping.
pmp
NAT-PMP discovery and port mapping.
protocol
The BEP protocol.
relay
Relay interaction (strelaysrv).
upnp
UPnP discovery and port mapping.
Other facilities:
fs
Filesystem access.
events
Event generation and logging.
http
REST API.
sha256
SHA256 hashing package (this facility currently unused).
stats
Persistent device and folder statistics.
sync
Mutexes. Used for debugging race conditions and deadlocks.
upgrade
Binary upgrades.
walkfs
Filesystem access while walking.
all
All of the above.
STBLOCKPROFILE
Write block profiles to block-$pid-$timestamp.pprof every 20 seconds.
STCPUPROFILE
Write a CPU profile to cpu-$pid.pprof on exit.
STDEADLOCKTIMEOUT
Used for debugging internal deadlocks; sets debug sensitivity. Use only under direction of a developer.
STDEADLOCKTHRESHOLD
Used for debugging internal deadlocks; sets debug sensitivity. Use only under direction of a developer.
STGUIASSETS
Directory to load GUI assets from. Overrides compiled in assets. Useful for developing webgui, commonly use STGUIASSETS=gui bin/syncthing.
STHASHING
Specify which hashing package to use. Defaults to automatic based on performance. Specify “minio” (compatibility) or “standard” for the default Go implementation.
STHEAPPROFILE
Write heap profiles to heap-$pid-$timestamp.pprof each time heap usage increases.
STNODEFAULTFOLDER
Don’t create a default folder when starting for the first time. This variable will be ignored anytime after the first run.
STNORESTART
Equivalent to the -no-restart flag. Disable the Syncthing monitor process which handles restarts for some configuration changes, upgrades, crashes and also log file writing (stdout is still written).
STNOUPGRADE
Disable automatic upgrades.
STPROFILER
Set to a listen address such as “127.0.0.1:9090” to start the profiler with HTTP access, which then can be reached at http://localhost:9090/debug/pprof. See go tool pprof for more information.
STPERFSTATS
Write running performance statistics to perf-$pid.csv. Not supported on Windows.
STRECHECKDBEVERY
Time before folder statistics (file, dir, … counts) are recalculated from scratch. The given duration must be parseable by GO’s time.ParseDuration. If missing or not parseable, the default value of 1 month is used. To force recalculation on every startup, set it to 0.
GOMAXPROCS
Set the maximum number of CPU cores to use. Defaults to all available CPU cores.
GOGC
Percentage of heap growth at which to trigger GC. Default is 100. Lower numbers keep peak memory usage down, at the price of CPU usage (i.e. performance).

2.1.7. See Also

syncthing-config(5), syncthing-stignore(5), syncthing-device-ids(7), syncthing-security(7), syncthing-networking(7), syncthing-versioning(7), syncthing-faq(7)