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 | | --noGroupCache | bool | false | Disable extended ACL group membership caching | | --nonEmpty | bool | false | Allow mounting over a non-empty directory | | --noSUID | bool | false | Disable SUID / SGID special permissions | | --ro | bool | false | Mount read-only (implies --noATime) | | --rootSquash | bool | false | Map UID 0 / GID 0 to --rootSquashUID / --rootSquashGID (implies --acl) | | --rootSquashGID | uint32 | 65534 | GID to map root to when --rootSquash is set | | --rootSquashUID | uint32 | 65534 | UID 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 |

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 | |------|------|---------|-------------| | --dirtyCapacity | uint32 | auto | [internal] In-memory dirty block cache capacity in blocks. Default is memCapacity/4 (minimum 8). | | --diskFolder | string | ~/.flexfs/mount/cache/<pid> | On-disk block cache folder path | | --diskMaxBlockSize | uint64 | 262144 | 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. | | --diskQuota | string | (empty) | Maximum disk usage for the block cache (e.g. 5%, 64M, 10G). Empty or 0 disables the disk cache. | | --diskWriteback | bool | false | Enable disk cache writeback mode for latency mitigation | | --memCapacity | string | auto | [internal] In-memory block cache capacity. Accepts a percentage of system RAM (e.g. 2%), a human-readable size (e.g. 4G, 512M), or a plain number of blocks (e.g. 2000). Default is 2% of system RAM divided by block size (minimum 32 blocks). | | --poolCapacity | uint32 | auto | [internal] Block buffer pool capacity in blocks. Default is prefetchActive + dirtyActive (minimum 8). |

Tip

The default --diskFolder path is within the user’s home directory (~/.flexfs/mount/cache/<pid>). For better performance, consider pointing this to a path on a local SSD. The <pid> placeholder is replaced with the mount process ID.

Performance

| Flag | Type | Default | Description | |------|------|---------|-------------| | --asyncRead | bool | false | [internal] Enable FUSE async read support | | --dirtyActive | uint32 | auto | [internal] Maximum number of dirty blocks actively syncing. Default is half of dirtyCapacity (minimum 4). | | --maxBops | uint32 | auto | [internal] Maximum number of parallel block operations. Default is dirtyActive + prefetchActive. | | --noMaxPages | bool | false | [internal] Limit FUSE max_pages to 32 instead of the kernel maximum | | --noPrefetch | bool | false | [internal] Disable block prefetching entirely | | --prefetchActive | uint32 | auto | [internal] Maximum number of active block prefetches. Default is memCapacity/8. |

FUSE tuning

| Flag | Type | Default | Description | |------|------|---------|-------------| | --attrValid | uint64 | 28800 | [internal] Seconds to cache file/directory attributes | | --attrValidNsec | uint32 | 0 | [internal] Nanosecond offset for --attrValid | | --dirPageSize | uint32 | 5000 | [internal] Directory stream page size | | --dirTTL | uint32 | 10 | [internal] Seconds to cache directory stream pages | | --entryValid | uint64 | 1 | [internal] Seconds to cache directory entries | | --entryValidNsec | uint32 | 0 | [internal] Nanosecond offset for --entryValid | | --longNames | bool | false | [internal] Allow names up to 1023 characters (default limit is 255) |

Networking and proxy

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

Credentials and auth

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

Update control

| Flag | Type | Default | Description | |------|------|---------|-------------| | --noRemount | bool | false | Disable automatic remount after an update (the mount will stop instead) | | --noUpdate | bool | false | Disable the automatic update mechanism (implies --noRemount) | | --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 | |------|------|---------|-------------| | --blockRTT | bool | false | [internal] Log all block storage round-trip times | | --foreground / -f | bool | false | Run in foreground mode instead of daemonizing (implies --noRemount) | | --fuseRTT | bool | false | [internal] Log all FUSE round-trip times | | --logFile | string | ~/.flexfs/mount/logs/<name>-<pid>.log | Log file path in daemon mode. The <name> and <pid> placeholders are replaced at startup. | | --memStats | bool | false | [internal] Log buffer pool and LRU cache statistics | | --metaRTT | bool | false | [internal] Log all metadata server round-trip times | | --pprof | bool | false | [internal] Enable the Go pprof profiler | | --pprofPort | int | 6063 | [internal] Pprof server port | | --storeRTT | bool | false | [internal] Log all store subsystem round-trip times | | --verbose / -v | bool | false | Enable verbose logging (implies all RTT and memStats logging) |

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.