{ "mode": "man", "parameter": "mount.fuse3", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/mount.fuse3/8/json", "generated": "2026-10-08T19:45:17Z", "sections": { "NAME": { "content": "fuse - configuration and mount options for FUSE file systems\n", "subsections": [] }, "DESCRIPTION": { "content": "FUSE (Filesystem in Userspace) is a simple interface for userspace programs to export a vir‐\ntual filesystem to the Linux kernel. FUSE also aims to provide a secure method for non privi‐\nleged users to create and mount their own filesystem implementations.\n", "subsections": [] }, "DEFINITIONS": { "content": "FUSE The in-kernel filesystem that forwards requests to a user-space process.\n", "subsections": [ { "name": "filesystem", "content": "The user-space process that responds to requests received from the kernel.\n" }, { "name": "libfuse", "content": "The shared library that most (user-space) filesystems use to communicate with FUSE\n(the kernel filesystem). libfuse also provides the fusermount3 (or fusermount if you\nhave older version of libfuse) helper to allow non-privileged users to mount filesys‐\ntems.\n" }, { "name": "filesystem owner", "content": "The user that starts the filesystem and instructs the kernel to associate it with a\nparticular mountpoint. The latter is typically done by the filesystem itself on start-\nup. When using libfuse, this is done by calling the fusermount3 utility.\n\nclient Any process that interacts with the mountpoint.\n" } ] }, "CONFIGURATION": { "content": "Some options regarding mount policy can be set in the file /etc/fuse.conf. Currently these\noptions are:\n", "subsections": [ { "name": "mount_max = NNN", "content": "Set the maximum number of FUSE mounts allowed to non-root users. The default is 1000.\n" }, { "name": "user_allow_other", "content": "Allow non-root users to specify the allowother or allowroot mount options (see be‐\nlow).\n\nThese limits are enforced by the fusermount3 helper, so they can be avoided by filesystems\nthat run as root.\n" } ] }, "OPTIONS": { "content": "Most of the generic mount options described in mount are supported (ro, rw, suid, nosuid,\ndev, nodev, exec, noexec, atime, noatime, sync, async, dirsync). Filesystems are mounted with\nnodev,nosuid by default, which can only be overridden by a privileged user.\n", "subsections": [ { "name": "General mount options:", "content": "These are FUSE specific mount options that can be specified for all filesystems:\n" }, { "name": "default_permissions", "content": "This option instructs the kernel to perform its own permission check instead of defer‐\nring all permission checking to the filesystem. The check by the kernel is done in ad‐\ndition to any permission checks by the filesystem, and both have to succeed for an op‐\neration to be allowed. The kernel performs a standard UNIX permission check (based on\nmode bits and ownership of the directory entry, and uid/gid of the client).\n\nThis mount option is activated implicitly if the filesystem enables ACL support during\nthe initial feature negotiation when opening the device fd. In this case, the kernel\nperforms both ACL and standard unix permission checking.\n\nFilesystems that do not implement any permission checking should generally add this\noption internally.\n" }, { "name": "allow_other", "content": "This option overrides the security measure restricting file access to the filesystem\nowner, so that all users (including root) can access the files.\n" }, { "name": "rootmode=M", "content": "Specifies the file mode of the filesystem's root (in octal representation).\n\nblkdev Mount a filesystem backed by a block device. This is a privileged option. The device\nmust be specified with the fsname=NAME option.\n" }, { "name": "blksize=N", "content": "Set the block size for the filesystem. This option is only valid for 'fuseblk' type\nmounts. The default is 512.\n\nIn most cases, this option should not be specified by the filesystem owner but set in‐\nternally by the filesystem.\n" }, { "name": "max_read=N", "content": "With this option the maximum size of read operations can be set. The default is infi‐\nnite, but typically the kernel enforces its own limit in addition to this one. A value\nof zero corresponds to no limit.\n\nThis option should not be specified by the filesystem owner. The correct (or optimum)\nvalue depends on the filesystem implementation and should thus be set by the filesys‐\ntem internally.\n\nThis mount option is deprecated in favor of direct negotiation over the device fd (as\ndone for e.g. the maximum size of write operations). For the time being, libfuse-using\nfilesystems that want to limit the read size must therefore use this mount option and\nset the same value again in the init() handler.\n\nfd=N The file descriptor to use for communication between the userspace filesystem and the\nkernel. The file descriptor must have been obtained by opening the FUSE device\n(/dev/fuse).\n\nThis option should not be specified by the filesystem owner. It is set by libfuse (or,\nif libfuse is not used, must be set by the filesystem itself).\n" }, { "name": "user_id=N", "content": "groupid=N Specifies the numeric uid/gid of the mount owner.\n\nThis option should not be specified by the filesystem owner. It is set by libfuse (or,\nif libfuse is not used, must be set by the filesystem itself).\n" }, { "name": "fsname=NAME", "content": "Sets the filesystem source (first field in /etc/mtab). The default is the name of the\nfilesystem process.\n" }, { "name": "subtype=TYPE", "content": "Sets the filesystem type (third field in /etc/mtab). The default is the name of the\nfilesystem process. If the kernel supports it, /etc/mtab and /proc/mounts will show\nthe filesystem type as fuse.TYPE\n\nIf the kernel doesn't support subtypes, the source field will be TYPE#NAME, or if fs‐\nname option is not specified, just TYPE.\n\n" }, { "name": "libfuse-specific mount options:", "content": "These following options are not actually passed to the kernel but interpreted by libfuse.\nThey can be specified for all filesystems that use libfuse:\n" }, { "name": "allow_root", "content": "This option is similar to allowother but file access is limited to the filesystem\nowner and root. This option and allowother are mutually exclusive.\n" }, { "name": "auto_unmount", "content": "This option enables automatic release of the mountpoint if filesystem terminates for\nany reason. Normally the filesystem is responsible for releasing the mountpoint, which\nmeans that the mountpoint becomes inaccessible if the filesystem terminates without\nfirst unmounting.\n\nAt the moment, this option implies that the filesystem will also be mounted with nodev\nand nosuid (even when mounted by root). This restriction may be lifted in the future.\n\n" }, { "name": "High-level mount options:", "content": "These following options are not actually passed to the kernel but interpreted by libfuse.\nThey can only be specified for filesystems that use the high-level libfuse API:\n" }, { "name": "kernel_cache", "content": "This option disables flushing the cache of the file contents on every open(2). This\nshould only be enabled on filesystems, where the file data is never changed externally\n(not through the mounted FUSE filesystem). Thus it is not suitable for network\nfilesystems and other \"intermediate\" filesystems.\n\nNOTE: if this option is not specified (and neither directio) data is still cached af‐\nter the open(2), so a read(2) system call will not always initiate a read operation.\n" }, { "name": "auto_cache", "content": "This option is an alternative to kernelcache. Instead of unconditionally keeping\ncached data, the cached data is invalidated on open(2) if the modification time or the\nsize of the file has changed since it was last opened.\n" }, { "name": "umask=M", "content": "Override the permission bits in stmode set by the filesystem. The resulting permis‐\nsion bits are the ones missing from the given umask value. The value is given in oc‐\ntal representation.\n\nuid=N Override the stuid field set by the filesystem (N is numeric).\n\ngid=N Override the stgid field set by the filesystem (N is numeric).\n" }, { "name": "entry_timeout=T", "content": "The timeout in seconds for which name lookups will be cached. The default is 1.0 sec‐\nond. For all the timeout options, it is possible to give fractions of a second as well\n(e.g. entrytimeout=2.8)\n" }, { "name": "negative_timeout=T", "content": "The timeout in seconds for which a negative lookup will be cached. This means, that if\nfile did not exist (lookup returned ENOENT), the lookup will only be redone after the\ntimeout, and the file/directory will be assumed to not exist until then. The default\nis 0.0 second, meaning that caching negative lookups are disabled.\n" }, { "name": "attr_timeout=T", "content": "The timeout in seconds for which file/directory attributes are cached. The default is\n1.0 second.\n" }, { "name": "ac_attr_timeout=T", "content": "The timeout in seconds for which file attributes are cached for the purpose of check‐\ning if autocache should flush the file data on open. The default is the value of\nattrtimeout\n" }, { "name": "noforget", "content": "" }, { "name": "remember=T", "content": "Normally, libfuse assigns inodes to paths only for as long as the kernel is aware of\nthem. With this option inodes are instead assigned for at least T seconds (or, in the\ncase of noforget, the life-time of the filesystem). This will require more memory, but\nmay be necessary when using applications that make use of inode numbers.\n" }, { "name": "modules=M1[:M2...]", "content": "Add modules to the filesystem stack. Modules are pushed in the order they are speci‐\nfied, with the original filesystem being on the bottom of the stack.\n\n" }, { "name": "mount.fuse3 options:", "content": "These options are interpreted by mount.fuse3 and are thus only available when mounting a file\nsystem via mount.fuse3 (such as when mounting via the generic mount(1) command or\n/etc/fstab). Supported options are:\n" }, { "name": "setuid=USER", "content": "Switch to USER and its primary group before launching the FUSE file system process.\nmount.fuse3 must be run as root or with CAPSETUID and CAPSETGID for this to work.\n" }, { "name": "drop_privileges", "content": "Perform setup of the FUSE file descriptor and mounting the file system before launch‐\ning the FUSE file system process. mount.fuse3 requires privilege to do so, i.e. must\nbe run as root or at least with CAPSYSADMIN and CAPSETPCAP. It will launch the file\nsystem process fully unprivileged, i.e. without capabilities(7) and prctl(2) flags set\nup such that privileges can't be reacquired (e.g. via setuid or fscaps binaries). This\nreduces risk in the event of the FUSE file system process getting compromised by mali‐\ncious file system data.\n\n\nFUSE MODULES (STACKING)\nModules are filesystem stacking support to high level API. Filesystem modules can be built\ninto libfuse or loaded from shared object\n" }, { "name": "iconv", "content": "Perform file name character set conversion. Options are:\n" }, { "name": "from_code=CHARSET", "content": "Character set to convert from (see iconv -l for a list of possible values). Default is\nUTF-8.\n" }, { "name": "to_code=CHARSET", "content": "Character set to convert to. Default is determined by the current locale.\n" }, { "name": "subdir", "content": "Prepend a given directory to each path. Options are:\n" }, { "name": "subdir=DIR", "content": "Directory to prepend to all paths. This option is mandatory.\n" }, { "name": "rellinks", "content": "Transform absolute symlinks into relative\n" }, { "name": "norellinks", "content": "Do not transform absolute symlinks into relative. This is the default.\n" } ] }, "SECURITY": { "content": "The fusermount3 program is installed set-user-gid to fuse. This is done to allow users from\nfuse group to mount their own filesystem implementations. There must however be some limita‐\ntions, in order to prevent Bad User from doing nasty things. Currently those limitations\nare:\n\n1. The user can only mount on a mountpoint, for which it has write permission\n\n2. The mountpoint is not a sticky directory which isn't owned by the user (like /tmp usu‐\nally is)\n\n3. No other user (including root) can access the contents of the mounted filesystem.\n", "subsections": [] }, "NOTE": { "content": "FUSE filesystems are unmounted using the fusermount3(1) command (fusermount3 -u mountpoint).\n", "subsections": [] }, "AUTHORS": { "content": "FUSE is currently maintained by Nikolaus Rath \n\nThe original author of FUSE is Miklos Szeredi .\n\nThis man page was originally written by Bastien Roucaries for the Debian GNU/Linux distribution.\n", "subsections": [] }, "SEE ALSO": { "content": "fusermount3(1) fusermount(1) mount(8) fuse(4)\n\nfuse(8)", "subsections": [] } }, "summary": "fuse - configuration and mount options for FUSE file systems", "flags": [], "examples": [], "see_also": [ { "name": "fusermount3", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/fusermount3/1/json" }, { "name": "fusermount", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/fusermount/1/json" }, { "name": "mount", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/mount/8/json" }, { "name": "fuse", "section": "4", "url": "https://www.chedong.com/phpMan.php/man/fuse/4/json" }, { "name": "fuse", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/fuse/8/json" } ] }