1fuse(8) System Manager's Manual fuse(8)
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6 fuse - format and options for the fuse file systems
7
9 FUSE (Filesystem in Userspace) is a simple interface for userspace pro‐
10 grams to export a virtual filesystem to the Linux kernel. FUSE also
11 aims to provide a secure method for non privileged users to create and
12 mount their own filesystem implementations.
13
15 Some options regarding mount policy can be set in the file
16 /etc/fuse.conf. Currently these options are:
17 mount_max = NNN
19 Set the maximum number of FUSE mounts allowed to non-root users.
20 The default is 1000.
21 user_allow_other
23 Allow non-root users to specify the allow_other or allow_root
24 mount options (see below).
25
27 Most of the generic mount options described in mount are supported (ro,
28 rw, suid, nosuid, dev, nodev, exec, noexec, atime, noatime, sync,
29 async, dirsync). Filesystems are mounted with nodev,nosuid by default,
30 which can only be overridden by a privileged user.
31 General mount options:
33 These are FUSE specific mount options that can be specified for all
34 filesystems:
35 default_permissions
37 By default FUSE doesn't check file access permissions, the
38 filesystem is free to implement it's access policy or leave it
39 to the underlying file access mechanism (e.g. in case of network
40 filesystems). This option enables permission checking, restrict‐
41 ing access based on file mode. This is option is usually useful
42 together with the allow_other mount option.
43 allow_other
45 This option overrides the security measure restricting file
46 access to the user mounting the filesystem. So all users
47 (including root) can access the files. This option is by
48 default only allowed to root, but this restriction can be
49 removed with a configuration option described in the previous
50 section.
51 allow_root
53 This option is similar to allow_other but file access is limited
54 to the user mounting the filesystem and root. This option and
55 allow_other are mutually exclusive.
56 kernel_cache
58 This option disables flushing the cache of the file contents on
59 every open(2). This should only be enabled on filesystems,
60 where the file data is never changed externally (not through the
61 mounted FUSE filesystem). Thus it is not suitable for network
62 filesystems and other intermediate filesystems.
63 NOTE: if this option is not specified (and neither direct_io)
65 data is still cached after the open(2), so a read(2) system call
66 will not always initiate a read operation.
67 auto_cache
69 This option enables automatic flushing of the data cache on
70 open(2). The cache will only be flushed if the modification time
71 or the size of the file has changed.
72 large_read
74 Issue large read requests. This can improve performance for
75 some filesystems, but can also degrade performance. This option
76 is only useful on 2.4.X kernels, as on 2.6 kernels requests size
77 is automatically determined for optimum performance.
78 direct_io
80 This option disables the use of page cache (file content cache)
81 in the kernel for this filesystem. This has several affects:
82 1. Each read(2) or write(2) system call will initiate one or more
84 read or write operations, data will not be cached in the kernel.
85 2. The return value of the read() and write() system calls will
87 correspond to the return values of the read and write opera‐
88 tions. This is useful for example if the file size is not known
89 in advance (before reading it).
90 max_read=N
92 With this option the maximum size of read operations can be set.
93 The default is infinite. Note that the size of read requests is
94 limited anyway to 32 pages (which is 128kbyte on i386).
95 max_readahead=N
97 Set the maximum number of bytes to read-ahead. The default is
98 determined by the kernel. On linux-2.6.22 or earlier it's 131072
99 (128kbytes)
100 max_write=N
102 Set the maximum number of bytes in a single write operation. The
103 default is 128kbytes. Note, that due to various limitations,
104 the size of write requests can be much smaller (4kbytes). This
105 limitation will be removed in the future.
106 async_read
108 Perform reads asynchronously. This is the default
109 sync_read
111 Perform all reads (even read-ahead) synchronously.
112 hard_remove
114 The default behavior is that if an open file is deleted, the
115 file is renamed to a hidden file (.fuse_hiddenXXX), and only
116 removed when the file is finally released. This relieves the
117 filesystem implementation of having to deal with this problem.
118 This option disables the hiding behavior, and files are removed
119 immediately in an unlink operation (or in a rename operation
120 which overwrites an existing file).
121 It is recommended that you not use the hard_remove option. When
123 hard_remove is set, the following libc functions fail on
124 unlinked files (returning errno of ENOENT): read(2), write(2),
125 fsync(2), close(2), f*xattr(2), ftruncate(2), fstat(2), fch‐
126 mod(2), fchown(2)
127 debug Turns on debug information printing by the library.
129 fsname=NAME
131 Sets the filesystem source (first field in /etc/mtab). The
132 default is the mount program name.
133 subtype=TYPE
135 Sets the filesystem type (third field in /etc/mtab). The default
136 is the mount program name. If the kernel suppports it, /etc/mtab
137 and /proc/mounts will show the filesystem type as fuse.TYPE
138 If the kernel doesn't support subtypes, the source filed will be
140 TYPE#NAME, or if fsname option is not specified, just TYPE.
141 use_ino
143 Honor the st_ino field in kernel functions getattr() and
144 fill_dir(). This value is used to fill in the st_ino field in
145 the stat(2), lstat(2), fstat(2) functions and the d_ino field in
146 the readdir(2) function. The filesystem does not have to guaran‐
147 tee uniqueness, however some applications rely on this value
148 being unique for the whole filesystem.
149 readdir_ino
151 If use_ino option is not given, still try to fill in the d_ino
152 field in readdir(2). If the name was previously looked up, and
153 is still in the cache, the inode number found there will be
154 used. Otherwise it will be set to -1. If use_ino option is
155 given, this option is ignored.
156 nonempty
158 Allows mounts over a non-empty file or directory. By default
159 these mounts are rejected to prevent accidental covering up of
160 data, which could for example prevent automatic backup.
161 umask=M
163 Override the permission bits in st_mode set by the filesystem.
164 The resulting permission bits are the ones missing from the
165 given umask value. The value is given in octal representation.
166 uid=N Override the st_uid field set by the filesystem (N is numeric).
168 gid=N Override the st_gid field set by the filesystem (N is numeric).
170 blkdev Mount a filesystem backed by a block device. This is a privi‐
172 leged option. The device must be specified with the fsname=NAME
173 option.
174 entry_timeout=T
176 The timeout in seconds for which name lookups will be cached.
177 The default is 1.0 second. For all the timeout options, it is
178 possible to give fractions of a second as well (e.g. entry_time‐
179 out=2.8)
180 negative_timeout=T
182 The timeout in seconds for which a negative lookup will be
183 cached. This means, that if file did not exist (lookup retuned
184 ENOENT), the lookup will only be redone after the timeout, and
185 the file/directory will be assumed to not exist until then. The
186 default is 0.0 second, meaning that caching negative lookups are
187 disabled.
188 attr_timeout=T
190 The timeout in seconds for which file/directory attributes are
191 cached. The default is 1.0 second.
192 ac_attr_timeout=T
194 The timeout in seconds for which file attributes are cached for
195 the purpose of checking if auto_cache should flush the file data
196 on open. The default is the value of attr_timeout
197 intr Allow requests to be interrupted. Turning on this option may
199 result in unexpected behavior, if the filesystem does not sup‐
200 port request interruption.
201 intr_signal=NUM
203 Specify which signal number to send to the filesystem when a
204 request is interrupted. The default is hardcoded to USR1.
205 modules=M1[:M2...]
207 Add modules to the filesystem stack. Modules are pushed in the
208 order they are specified, with the original filesystem being on
209 the bottom of the stack.
210
212 Modules are filesystem stacking support to high level API. Filesystem
213 modules can be built into libfuse or loaded from shared object
214 iconv
216 Perform file name character set conversion. Options are:
217 from_code=CHARSET
219 Character set to convert from (see iconv -l for a list of possi‐
220 ble values). Default is UTF-8.
221 to_code=CHARSET
223 Character set to convert to. Default is determined by the cur‐
224 rent locale.
225 subdir
227 Prepend a given directory to each path. Options are:
228 subdir=DIR
230 Directory to prepend to all paths. This option is mandatory.
231 rellinks
233 Transform absolute symlinks into relative
234 norellinks
236 Do not transform absolute symlinks into relative. This is the
237 default.
238
240 The fusermount program is installed set-user-gid to fuse. This is done
241 to allow users from fuse group to mount their own filesystem implemen‐
242 tations. There must however be some limitations, in order to prevent
243 Bad User from doing nasty things. Currently those limitations are:
244 1. The user can only mount on a mountpoint, for which it has write
246 permission
247 2. The mountpoint is not a sticky directory which isn't owned by
249 the user (like /tmp usually is)
250 3. No other user (including root) can access the contents of the
252 mounted filesystem.
253
255 FUSE filesystems are unmounted using the fusermount(1) command (fuser‐
256 mount -u mountpoint).
257
259 The main author of FUSE is Miklos Szeredi <mszeredi@inf.bme.hu>.
260 This man page was written by Bastien Roucaries <rou‐
262 caries.bastien+debian@gmail.com> for the Debian GNU/Linux distribution
263 (but it may be used by others) from README file.
264
266 fusermount(1) mount(8)
267 fuse(8)