Manpages - mount.fuse3.8

These are FUSE specific mount options that can be specified for all filesystems:

default_permissions

This option instructs the kernel to perform its own permission check instead of deferring all permission checking to the filesystem. The check by the kernel is done in addition to any permission checks by the filesystem, and both have to succeed for an operation to be allowed. The kernel performs a standard UNIX permission check (based on mode bits and ownership of the directory entry, and uid/gid of the client).

This mount option is activated implicitly if the filesystem enables ACL support during the initial feature negotiation when opening the device fd. In this case, the kernel performs both ACL and standard unix permission checking.

Filesystems that do not implement any permission checking should generally add this option internally.

allow_other

This option overrides the security measure restricting file access to the filesystem owner, so that all users (including root) can access the files.

rootmode=M

Specifies the file mode of the filesystem’s root (in octal representation).

blkdev

Mount a filesystem backed by a block device. This is a privileged option. The device must be specified with the fsname=NAME option.

blksize=N

Set the block size for the filesystem. This option is only valid for ’fuseblk’ type mounts. The default is 512.

In most cases, this option should not be specified by the filesystem owner but set internally by the filesystem.

max_read=N

With this option the maximum size of read operations can be set. The default is infinite, but typically the kernel enforces its own limit in addition to this one. A value of zero corresponds to no limit.

This option should not be specified by the filesystem owner. The correct (or optimum) value depends on the filesystem implementation and should thus be set by the filesystem internally.

This mount option is deprecated in favor of direct negotiation over the device fd (as done for e.g. the maximum size of write operations). For the time being, libfuse-using filesystems that want to limit the read size must therefore use this mount option and set the same value again in the init() handler.

fd=N

The file descriptor to use for communication between the userspace filesystem and the kernel. The file descriptor must have been obtained by opening the FUSE device (/dev/fuse).

This option should not be specified by the filesystem owner. It is set by libfuse (or, if libfuse is not used, must be set by the filesystem itself).

user_id=N

group_id=N Specifies the numeric uid/gid of the mount owner.

This option should not be specified by the filesystem owner. It is set by libfuse (or, if libfuse is not used, must be set by the filesystem itself).

fsname=NAME

Sets the filesystem source (first field in /etc/mtab). The default is the name of the filesystem process.

subtype=TYPE

Sets the filesystem type (third field in /etc/mtab). The default is the name of the filesystem process. If the kernel supports it, /etc/mtab and /proc/mounts will show the filesystem type as fuse.TYPE

If the kernel doesn’t support subtypes, the source field will be TYPE#NAME, or if fsname option is not specified, just TYPE.

These following options are not actually passed to the kernel but interpreted by libfuse. They can be specified for all filesystems that use libfuse:

allow_root

This option is similar to allow_other but file access is limited to the filesystem owner and root. This option and allow_other are mutually exclusive.

auto_unmount

This option enables automatic release of the mountpoint if filesystem terminates for any reason. Normally the filesystem is responsible for releasing the mountpoint, which means that the mountpoint becomes inaccessible if the filesystem terminates without first unmounting.

At the moment, this option implies that the filesystem will also be mounted with nodev and nosuid (even when mounted by root). This restriction may be lifted in the future.

These following options are not actually passed to the kernel but interpreted by libfuse. They can only be specified for filesystems that use the high-level libfuse API:

kernel_cache

This option disables flushing the cache of the file contents on every *open*(2). This should only be enabled on filesystems, where the file data is never changed externally (not through the mounted FUSE filesystem). Thus it is not suitable for network filesystems and other “intermediate” filesystems.

NOTE: if this option is not specified (and neither direct_io) data is still cached after the *open*(2), so a *read*(2) system call will not always initiate a read operation.

auto_cache

This option is an alternative to kernel_cache. Instead of unconditionally keeping cached data, the cached data is invalidated on *open*(2) if the modification time or the size of the file has changed since it was last opened.

umask=M

Override the permission bits in st_mode set by the filesystem. The resulting permission bits are the ones missing from the given umask value. The value is given in octal representation.

uid=N

Override the st_uid field set by the filesystem (N is numeric).

gid=N

Override the st_gid field set by the filesystem (N is numeric).

entry_timeout=T

The timeout in seconds for which name lookups will be cached. The default is 1.0 second. For all the timeout options, it is possible to give fractions of a second as well (e.g. entry_timeout=2.8)

negative_timeout=T

The timeout in seconds for which a negative lookup will be cached. This means, that if file did not exist (lookup returned ENOENT), the lookup will only be redone after the timeout, and the file/directory will be assumed to not exist until then. The default is 0.0 second, meaning that caching negative lookups are disabled.

attr_timeout=T

The timeout in seconds for which file/directory attributes are cached. The default is 1.0 second.

ac_attr_timeout=T

The timeout in seconds for which file attributes are cached for the purpose of checking if auto_cache should flush the file data on open. The default is the value of attr_timeout

noforget

remember=T

Normally, libfuse assigns inodes to paths only for as long as the kernel is aware of them. With this option inodes are instead assigned for at least T seconds (or, in the case of noforget, the life-time of the filesystem). This will require more memory, but may be necessary when using applications that make use of inode numbers.

modules=M1[:M2…]

Add modules to the filesystem stack. Modules are pushed in the order they are specified, with the original filesystem being on the bottom of the stack.

These options are interpreted by mount.fuse3 and are thus only available when mounting a file system via mount.fuse3 (such as when mounting via the generic *mount*(1) command or /etc/fstab). Supported options are:

setuid=USER

Switch to USER and its primary group before launching the FUSE file system process. mount.fuse3 must be run as root or with CAP_SETUID and CAP_SETGID for this to work.

drop_privileges

Perform setup of the FUSE file descriptor and mounting the file system before launching the FUSE file system process. mount.fuse3 requires privilege to do so, i.e. must be run as root or at least with CAP_SYS_ADMIN and CAP_SETPCAP. It will launch the file system process fully unprivileged, i.e. without *capabilities*(7) and *prctl*(2) flags set up such that privileges can’t be reacquired (e.g. via setuid or fscaps binaries). This reduces risk in the event of the FUSE file system process getting compromised by malicious file system data.

Perform file name character set conversion. Options are:

from_code=CHARSET

Character set to convert from (see iconv -l for a list of possible values). Default is UTF-8.

to_code=CHARSET

Character set to convert to. Default is determined by the current locale.

Prepend a given directory to each path. Options are:

subdir=DIR

Directory to prepend to all paths. This option is mandatory.

rellinks

Transform absolute symlinks into relative

norellinks

Do not transform absolute symlinks into relative. This is the default.