sshfs.1 - Online Linux Manual Page

SSHFS - Online Linux Manual PageSection : 1
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Note : User Commands

NAMESSHFS − filesystem client based on SSH

SYNOPSISTo mount a filesystem: sshfs [user@]host:[dir] mountpoint [options] If host is a numeric IPv6 address, it needs to be enclosed in square brackets. To unmount it: fusermount3 −u mountpoint # Linux umount mountpoint # OS X, FreeBSD

DESCRIPTIONSSHFS allows you to mount a remote filesystem using SSH (more precisely, the SFTP subsystem). Most SSH servers support and enable this SFTP access by default, so SSHFS is very simple to use − there's nothing to do on the server−side. By default, file permissions are ignored by SSHFS. Any user that can access the filesystem will be able to perform any operation that the remote server permits − based on the credentials that were used to connect to the server. If this is undesired, local permission checking can be enabled with −o default_permissions. By default, only the mounting user will be able to access the filesystem. Access for other users can be enabled by passing −o allow_other. In this case you most likely also want to use −o default_permissions. It is recommended to run SSHFS as regular user (not as root). For this to work the mountpoint must be owned by the user. If username is omitted SSHFS will use the local username. If the directory is omitted, SSHFS will mount the (remote) home directory. If you need to enter a password sshfs will ask for it (actually it just runs ssh which ask for the password if needed).

OPTIONS −o opt,[opt...] mount options, see below for details. A a variety of SSH options can be given here as well, see the manual pages for sftp(1) and ssh_config(5). −h, −−help print help and exit. −V, −−version print version information and exit. −d, −−debug print debugging information. −p PORT equivalent to '−o port=PORT' −f do not daemonize, stay in foreground. −s Single threaded operation. −C equivalent to '−o compression=yes' −F ssh_configfile specifies alternative ssh configuration file −1 equivalent to '−o ssh_protocol=1' −o reconnect automatically reconnect to server if connection is interrupted. Attempts to access files that were opened before the reconnection will give errors and need to be re−opened. −o delay_connect Don't immediately connect to server, wait until mountpoint is first accessed. −o sshfs_sync synchronous writes. This will slow things down, but may be useful in some situations. −o no_readahead Only read exactly the data that was requested, instead of speculatively reading more to anticipate the next read request. −o sync_readdir synchronous readdir. This will slow things down, but may be useful in some situations. −o workaround=LIST Enable the specified workaround. See the Caveats section below for some additional information. Possible values are: rename Emulate overwriting an existing file by deleting and renaming. renamexdev Make rename fail with EXDEV instead of the default EPERM to allow moving files across remote filesystems. truncate Work around servers that don't support truncate by coping the whole file, truncating it locally, and sending it back. fstat Work around broken servers that don't support fstat() by using stat instead. buflimit Work around OpenSSH "buffer fillup" bug. createmode Work around broken servers that produce an error when passing a non−zero mode to create, by always passing a mode of 0. −o idmap=TYPE How to map remote UID/GIDs to local values. Possible values are: none no translation of the ID space (default). user map the UID/GID of the remote user to UID/GID of the mounting user. file translate UIDs/GIDs based upon the contents of −−uidfile and −−gidfile. −o uidfile=FILE file containing username:uid mappings for −o idmap=file −o gidfile=FILE file containing groupname:gid mappings for −o idmap=file −o nomap=TYPE with idmap=file, how to handle missing mappings: ignore don't do any re−mapping error return an error (default) −o ssh_command=CMD execute CMD instead of 'ssh' −o ssh_protocol=N ssh protocol to use (default: 2) −o sftp_server=SERV path to sftp server or subsystem (default: sftp) −o directport=PORT directly connect to PORT bypassing ssh −o passive communicate over stdin and stdout bypassing network. Useful for mounting local filesystem on the remote side. An example using dpipe command would be dpipe /usr/lib/openssh/sftp−server = ssh RemoteHostname sshfs :/directory/to/be/shared ~/mnt/src −o passive −o disable_hardlink With this option set, attempts to call link(2) will fail with error code ENOSYS. −o transform_symlinks transform absolute symlinks on remote side to relative symlinks. This means that if e.g. on the server side /foo/bar/com is a symlink to /foo/blub, SSHFS will transform the link target to ../blub on the client side. −o follow_symlinks follow symlinks on the server, i.e. present them as regular files on the client. If a symlink is dangling (i.e, the target does not exist) the behavior depends on the remote server − the entry may appear as a symlink on the client, or it may appear as a regular file that cannot be accessed. −o no_check_root don't check for existence of 'dir' on server −o password_stdin read password from stdin (only for pam_mount!) −o dir_cache=BOOL Enables (yes) or disables (no) the SSHFS directory cache. The directory cache holds the names of directory entries. Enabling it allows readdir(3) system calls to be processed without network access. −o dcache_max_size=N sets the maximum size of the directory cache. −o dcache_timeout=N sets timeout for directory cache in seconds. −o dcache_{stat,link,dir}_timeout=N sets separate timeout for {attributes, symlinks, names} in the directory cache. −o dcache_clean_interval=N sets the interval for automatic cleaning of the directory cache. −o dcache_min_clean_interval=N sets the interval for forced cleaning of the directory cache when full. −o direct_io This option disables the use of page cache (file content cache) in the kernel for this filesystem. This has several affects: 1. Each read() or write() system call will initiate one or more read or write operations, data will not be cached in the kernel. 2. The return value of the read() and write() system calls will correspond to the return values of the read and write operations. This is useful for example if the file size is not known in advance (before reading it). e.g. /proc filesystem −o max_conns=N sets the maximum number of simultaneous SSH connections to use. Each connection is established with a separate SSH process. The primary purpose of this feature is to improve the responsiveness of the file system during large file transfers. When using more than once connection, the password_stdin and passive options can not be used, and the buflimit workaround is not supported. In addition, SSHFS accepts several options common to all FUSE file systems. These are described in the mount.fuse3 manpage (look for "general", "libfuse specific", and "high−level API" options).

CAVEATS / WORKAROUNDS

HardlinksIf the SSH server supports the hardlinks extension, SSHFS will allow you to create hardlinks. However, hardlinks will always appear as individual files when seen through an SSHFS mount, i.e. they will appear to have different inodes and an st_nlink value of 1.

RenameSome SSH servers do not support atomically overwriting the destination when renaming a file. In this case you will get an error when you attempt to rename a file and the destination already exists. A workaround is to first remove the destination file, and then do the rename. SSHFS can do this automatically if you call it with −o workaround=rename. However, in this case it is still possible that someone (or something) recreates the destination file after SSHFS has removed it, but before SSHFS had the time to rename the old file. In this case, the rename will still fail.

Permission denied when moving files across remote filesystemsMost SFTP servers return only a generic "failure" when failing to rename across filesystem boundaries (EXDEV). sshfs normally converts this generic failure to a permission denied error (EPERM). If the option −o workaround=renamexdev is given, generic failures will be considered EXDEV errors which will make programs like mv(1) attempt to actually move the file after the failed rename.

SSHFS hangs for no apparent reasonIn some cases, attempts to access the SSHFS mountpoint may freeze if no filesystem activity has occurred for some time. This is typically caused by the SSH connection being dropped because of inactivity without SSHFS being informed about that. As a workaround, you can try to mount with −o ServerAliveInterval=15. This will force the SSH connection to stay alive even if you have no activity.

SSHFS hangs after the connection was interruptedBy default, network operations in SSHFS run without timeouts, mirroring the default behavior of SSH itself. As a consequence, if the connection to the remote host is interrupted (e.g. because a network cable was removed), operations on files or directories under the mountpoint will block until the connection is either restored or closed altogether (e.g. manually). Applications that try to access such files or directories will generally appear to "freeze" when this happens. If it is acceptable to discard data being read or written, a quick workaround is to kill the responsible sshfs process, which will make any blocking operations on the mounted filesystem error out and thereby "unfreeze" the relevant applications. Note that force unmounting with fusermount −zu, on the other hand, does not help in this case and will leave read/write operations in the blocking state. For a more automatic solution, one can use the −o ServerAliveInterval=15 option mentioned above, which will drop the connection after not receiving a response for 3 * 15 = 45 seconds from the remote host. By also supplying −o reconnect, one can ensure that the connection is re−established as soon as possible afterwards. As before, this will naturally lead to loss of data that was in the process of being read or written at the time when the connection was interrupted.

MOUNTING FROM /ETC/FSTABTo mount an SSHFS filesystem from /etc/fstab, simply use sshfs as the file system type. (For backwards compatibility, you may also use fuse.sshfs).