Watchman looks for configuration files in two places:

  • The global configuration file /etc/watchman.json
  • The root specific configuration file .watchmanconfig

When watching a root, if a valid JSON file named .watchmanconfig is present in the root directory, watchman will load it and use it as a source of configuration information specific to that root.

The global configuration path can be changed by passing the --enable-conffile option to configure when you build watchman. This documentation refers to it as /etc/watchman.json throughout, just be aware that your particular installation may locate it elsewhere. In addition, the environmental variable $WATCHMAN_CONFIG_FILE will override the default location.

Changes to the .watchmanconfig or /etc/watchman.json files are not picked up automatically; you will need to remove and re-add the watch (for .watchmanconfig) or restart watchman (for /etc/watchman.json) for those changes to take effect.

Resolution / Scoping

There are three configuration scopes:

  • local - the option value is read from the .watchmanconfig file in the associated root.
  • global - the option value is read from the /etc/watchman.json file
  • fallback - the option value is read from the .watchmanconfig file. If the option was not present in the .watchmanconfig file, then read it from the /etc/watchman.json file.

This table shows the scoping and availability of the various options:

Option Scope Since version
settle local  
root_restrict_files global deprecated in 3.1
root_files global 3.1
enforce_root_files global 3.1
illegal_fstypes global 2.9.8
illegal_fstypes_advice global 2.9.8
ignore_vcs local 2.9.3
ignore_dirs local 2.9.3
gc_age_seconds local 2.9.4
gc_interval_seconds local 2.9.4
fsevents_latency fallback 3.2
idle_reap_age_seconds local 3.7
hint_num_files_per_dir fallback 3.9
hint_num_dirs fallback 4.6
suppress_recrawl_warnings fallback 4.7

Configuration Options

settle

Specifies the settle period in milliseconds. This controls how long the filesystem should be idle before dispatching triggers. The default value is 20 milliseconds.

root_files

Since 3.1.

Specifies a list of files that, if present in a directory, identify that directory as the root of a project.

If left unspecified, to aid in transitioning between versions, watchman will use the value of the now deprecated root_restrict_files configuration setting.

If neither root_files nor root_restrict_files is specified in the configuration, watchman will use a default value consisting of:

  • .git
  • .hg
  • .svn
  • .watchmanconfig

Watchman will add .watchmanconfig to whatever value is specified for this configuration value if it is not present.

This example causes only .watchmanconfig to be considered as a project root file:

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{
  "root_files": [".watchmanconfig"]
}

See the watch-project command for more information.

enforce_root_files

Since 3.1.

This is a boolean option that defaults to false. If it is set to true then the watch command will only succeed if the requested directory contains one of the files listed by the root_files configuration option, and the watch-project command will only succeed if a valid project root is found.

If left unspecified, to aid in transitioning between versions, watchman will check to see if the now deprecated root_restrict_files configuration setting is present. If it is found then the effective value of enforce_root_files is set to true.

root_restrict_files

Deprecated starting in version 3.1; use root_files and enforce_root_files to effect the same behavior.

Specifies a list of files, at least one of which should be present in a directory for watchman to add it as a root. By default there are no restrictions.

For example,

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{
  "root_restrict_files": [".git", ".hg"]
}

will allow watches only in the top level of Git or Mercurial repositories.

illegal_fstypes

Specifies a list of filesystem types that watchman is prohibited to attempt to watch. Watchman will determine the filesystem type of the root of a watch; if the typename is present in the illegal_fstypes list, the watch will be prohibited. You may also specify illegal_fstypes_advice as a string with additional advice to your user. The purpose of this configuration option is largely to prevent the use of Watchman on network mounted filesystems. On Linux systems, Watchman may not be able to determine the precise type name of a mounted filesystem. If the filesystem type is not known to watchman, it will be reported as unknown.

For example,

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{
  "illegal_fstypes": ["nfs", "cifs", "smb"],
  "illegal_fstypes_advice": "use a local directory"
}

will prevent watching dirs mounted on network filesystems and provide the advice to use a local directory. You may omit the illegal_fstypes_advice setting to use a default suggestion to relocate the directory to local disk.

ignore_vcs

Apply special VCS ignore logic to the set of named dirs. This option has a default value of [".git", ".hg", ".svn"]. Dirs that match this option are observed and watched using special shallow logic. The shallow watch allows watchman to mildly abuse the version control directories to store its query cookie files and to observe VCS locking activity without having to watch the entire set of VCS data for large trees.

ignore_dirs

Dirs that match are completely ignored by watchman. This is useful to ignore a directory that contains only build products and where file change notifications are unwanted because of the sheer volume of files.

For example,

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{
  "ignore_dirs": ["build"]
}

would ignore the build directory at the top level of the watched tree, and everything below it. It will never appear in the watchman query results for the tree.

On Linux systems, ignore_dirs is respected at the OS level; the kernel simply will not tell watchman about changes to ignored dirs. macOS and Windows have limited or no support for this, so watchman needs to process and ignore this class of change.

For large trees or especially busy build dirs, it is recommended that you move the busy build dirs out of the tree for more optimal performance.

Since version 2.9.9, if you list a dir in ignore_dirs that is also listed in ignore_vcs, the ignore_dirs placement will take precedence. This may not sound like a big deal, but since ignore_vcs is used as a hint to for the placement of cookie files, having these two options overlap in earlier versions would break watchman queries.

Since 4.6.

On macOS the first 8 items listed in ignore_dirs can be accelerated at the OS level. This means that changes to those paths are not even communicated to the watchman service. Entries beyond the first 8 are processed and ignored by watchman. If your workload is prone to recrawl events you will want to prioritize your ignore_dirs list so that the most busy ignored locations occupy the first 8 positions in this list.

gc_age_seconds

Deleted files (and dirs) older than this are periodically pruned from the internal view of the filesystem. Until they are pruned, they will be visible to queries but will have their exists field set to false. Once they are pruned, watchman will remember the most recent clock value of the pruned nodes. Any since queries based on a clock prior to the last prune clock will be treated as a fresh instance query. This allows a client to detect and choose how to handle the case where they have missed changes. See is_fresh_instance elsewhere in this document for more information. The default for this is 43200 (12 hours).

gc_interval_seconds

How often to check for, and prune out, deleted nodes per the gc_age_seconds option description above. The default for this is 86400 (24 hours). Set this to 0 to disable the periodic pruning operation.

fsevents_latency

Controls the latency parameter that is passed to FSEventStreamCreate on OS X. The value is measured in seconds. The fixed value of this parameter prior to version 3.2 of watchman was 0.0001 seconds. Starting in version 3.2 of watchman, the default is now 0.01 seconds and can be controlled on a per-root basis.

If you observe problems with kFSEventStreamEventFlagUserDropped increasing the latency parameter will allow the system to batch more change notifications together and operate more efficiently.

fsevents_try_resync

This is macOS specific.

Since 4.6.

Defaults to false. If set to true, if a watch receives a kFSEventStreamEventFlagUserDropped event, attempt to resync from the fsevents journal if it is available. The journal may not be available if one or more volumes are mounted read-only, if the administrator has purged the journal, or if the fsevents id numbers have rolled over.

This resync operation is advantageous because it effectively allows rewinding and replaying the event stream from a known point in time and avoids the need to recrawl the entire watch.

If this option is set to false, or if the journal is not available, the original strategy of recrawling the watched directory tree is used instead.

Since 4.7.

The default changed to true. In addition, this resync strategy is now also applied to kFSEventStreamEventFlagKernelDropped events.

idle_reap_age_seconds

Since 3.7.

How many seconds a watch can remain idle before becoming a candidate for reaping, measured in seconds. The default for this is 432000 (5 days). Set this to 0 to prevent reaping.

A watch is considered to be idle when it has had no commands that operate on it for idle_reap_age_seconds. If an idle watch has no triggers and no subscriptions then it will be cancelled, releasing the associated operating system resources, and removed from the state file.

hint_num_files_per_dir

Since 3.9.

Used to pre-size hash tables used to track files per directory. This is most impactful during the initial crawl of the filesystem. Setting this too small will increase the chance of a hash insert having a collision and drive up the cost of the insert and subsequent gets.

Prior to version 3.9 of watchman this value was fixed at 2. Starting in version 3.9 the default value is 64 and can be configured via this setting in the .watchmanconfig or the global /etc/watchman.json configuration file.

Setting this value very large increases the memory overhead per directory in the tree; the value is rounded up to the next power of two and pre-allocated in an array of pointers. On a 64-bit system multiply that number by 8 to arrive at the number of bytes of overhead (halve this on a 32-bit system). The overhead is doubled when using a case insensitive filesystem.

The ideal size from a time complexity perspective is the number of files in your largest directory. From a space complexity perspective, the ideal size is 1; you would pay the cost of the collisions during the initial crawl and have a more optimal memory usage. Since watchman is primarily employed as an accelerator, we’d recommend biasing towards using more memory and taking less time to run.

hint_num_dirs

Since 4.6

Used to pre-size hash tables that are used to track the total set of files in the entire watched tree. The default value for this is 131072.

The optimal size is a power-of-two larger than the number of directories in your tree; running find . -type d | wc -l will tell you the number that you have.

Making this number too large is potentially wasteful of memory. Making this number too small results in increased latency during crawling while the hash tables are rebuilt.

suppress_recrawl_warnings

Since 4.7

When set to true, watchman will not produce recrawl related warning fields in the response PDUs of various requests. The default is false; the intent is that someone in your organization should be aware of recrawls and be able to manage the configuration and workload. Some sites employ an alternative mechanism for sampling and reporting this to the right set of people and wish to disable the warning so that it doesn’t appear in front of users that are unable to make the appropriate configuration changes for themselves.