Mount Options

This page documents every flag accepted by mount.flexfs start. Flags marked [internal] are hidden from --help output and intended for advanced tuning or debugging.

POSIX and access control

Flag	Type	Default	Description
--acl	bool	false	Enable extended ACL support (implies --xAttr)
--noATime	bool	false	Do not update access times on file opens
--noExec	bool	false	Disallow execution of binaries
--noSUID	bool	false	Disable SUID / SGID special permissions
--nonEmpty	bool	false	Allow mounting over a non-empty directory
--ro	bool	false	Mount read-only (implies --noATime)
--rootSquash	bool	false	Map UID 0 / GID 0 to --rootSquashUID / --rootSquashGID (implies --acl)
--rootSquashUID	uint32	65534	UID to map root to when --rootSquash is set
--rootSquashGID	uint32	65534	GID to map root to when --rootSquash is set
--umask	string	(none)	Explicit umask override in octal notation (e.g. 0002)
--xAttr	bool	false	Enable extended attribute support
--noGroupCache	bool	false	Disable extended ACL group membership caching

Note

Many access control flags (acl, noATime, noExec, noSUID, rootSquash, nonEmpty, xAttr) can also be set at the volume level via configure.flexfs. Volume-level settings are combined with mount-level flags — if either side enables a flag, it takes effect.

Caching

Flag	Type	Default	Description
--diskFolder	string	/dev/shm/.flexfs-cache-<pid>	On-disk block cache folder path
--diskQuota	string	(empty)	Maximum disk usage for the block cache (e.g. 5%, 64M, 10G). Empty or 0 disables the disk cache.
--diskMaxBlockSize	uint64	131072	Maximum processed block size in bytes that will be cached to disk. Blocks larger than this after decompression are not cached. 0 means no limit.
--diskWriteback	bool	false	Enable disk cache writeback mode for latency mitigation
--memCapacity	uint32	auto	[internal] In-memory block cache capacity in blocks. Default is calculated as 2.5% of system RAM divided by block size (minimum 16).
--dirtyCapacity	uint32	auto	[internal] In-memory dirty block cache capacity in blocks. Default is 0.5% of RAM divided by block size, capped at cpuBops (minimum 4).
--poolCapacity	uint32	auto	[internal] Block buffer pool capacity in blocks. Default is prefetchActive + dirtyActive (minimum 8).

Tip

The default --diskFolder path uses /dev/shm (a tmpfs RAM disk on Linux). To use actual disk storage, change this to a path on a local SSD. The <pid> placeholder is replaced with the mount process ID.

Performance

Flag	Type	Default	Description
--maxBops	uint32	auto	[internal] Maximum number of parallel block operations. Default is calculated from CPU count, architecture, and block size.
--prefetchActive	uint32	auto	[internal] Maximum number of active block prefetches. Default is half of maxBops, capped at memCapacity/4 (minimum 4).
--dirtyActive	uint32	auto	[internal] Maximum number of dirty blocks actively syncing. Default is half of dirtyCapacity (minimum 4).
--noPrefetch	bool	false	[internal] Disable block prefetching entirely
--asyncRead	bool	false	[internal] Enable FUSE async read support
--noMaxPages	bool	false	[internal] Limit FUSE max_pages to 32 instead of the kernel maximum

FUSE tuning

Flag	Type	Default	Description
--attrValid	uint64	3600	[internal] Seconds to cache file/directory attributes
--attrValidNsec	uint32	0	[internal] Nanosecond offset for --attrValid
--entryValid	uint64	1	[internal] Seconds to cache directory entries
--entryValidNsec	uint32	0	[internal] Nanosecond offset for --entryValid
--dirPageSize	uint32	5000	[internal] Directory stream page size
--dirTTL	uint32	10	[internal] Seconds to cache directory stream pages
--longNames	bool	false	[internal] Allow names up to 1023 characters (default limit is 255)

Networking and proxy

Flag	Type	Default	Description
--noProxy	bool	false	[internal] Bypass proxy servers and connect directly to object storage
--noProxySSL	bool	false	[internal] Disable TLS for proxy server connections
--noMetaSSL	bool	false	[internal] Disable TLS for metadata server connections
--sse	bool	false	[internal] Enable S3 server-side encryption (AES256)

Credentials and auth

Flag	Type	Default	Description
--credsFile	string	~/.flexfs/mount/creds/<name>	Path to the credentials file. The <name> placeholder is replaced with the volume name.
--adminAddr	string	(from creds)	[internal] Admin server address (overrides the credentials file)
--token	string	(from creds)	[internal] Volume auth token (overrides the credentials file)
--secret	string	(from creds)	[internal] Volume encryption secret (overrides the credentials file)

Update control

Flag	Type	Default	Description
--noUpdate	bool	false	Disable the automatic update mechanism (implies --noRemount)
--noRemount	bool	false	Disable automatic remount after an update (the mount will stop instead)
--staging	bool	false	Check the staging channel for updates instead of production
--testVersion	string	(none)	[internal] Override build version for testing update handoff
--updateInterval	uint32	360	[internal] Seconds between auto-update checks

Logging and diagnostics

Flag	Type	Default	Description
--verbose / -v	bool	false	Enable verbose logging (implies all RTT and memStats logging)
--foreground / -f	bool	false	Run in foreground mode instead of daemonizing (implies --noRemount)
--logFile	string	~/.flexfs/mount/logs/<name>-<pid>.log	Log file path in daemon mode. The <name> and <pid> placeholders are replaced at startup.
--blockRTT	bool	false	[internal] Log all block storage round-trip times
--metaRTT	bool	false	[internal] Log all metadata server round-trip times
--storeRTT	bool	false	[internal] Log all store subsystem round-trip times
--fuseRTT	bool	false	[internal] Log all FUSE round-trip times
--memStats	bool	false	[internal] Log buffer pool and LRU cache statistics
--pprof	bool	false	[internal] Enable the Go pprof profiler

Time-travel

Flag	Type	Default	Description
--atTime	string	(none)	Mount the filesystem at a specific point in time in RFC 3339 format (e.g. 2025-06-15T14:30:00Z). Implies --ro. See Time-Travel Mounting.

Passing options via fstab

All flags can be passed as fstab mount options by removing the -- prefix. Boolean flags are set by name alone. For example:

my-volume  /mnt/data  flexfs  _netdev,nofail,ro,acl,verbose  0 0

See fstab Integration for details.