--- name: "fspick" section: "2" platform: "linux" package: "man-pages" version: "6.19-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/fspick" --- # fspick(2) select filesystem for reconfiguration ## NAME fspick - select filesystem for reconfiguration ## LIBRARY Standard C library (*libc*, *-lc*) ## SYNOPSIS ``` #include /* Definition of AT_* constants */ #include ``` **int fspick(int** *dirfd***, const char \****path***, unsigned int** *flags***);** ## DESCRIPTION The **fspick**() system call is part of the suite of file-descriptor-based mount facilities in Linux. **fspick**() creates a new filesystem configuration context for the extant filesystem instance associated with the path described by *dirfd* and *path*, places it into reconfiguration mode (similar to [**mount**(8)](/mount/8.md) with the **-o remount** option). A new file descriptor associated with the filesystem configuration context is then returned. The calling process must have the **CAP\_SYS\_ADMIN** capability in order to create a new filesystem configuration context. The resultant file descriptor can be used with [**fsconfig**(2)](/fsconfig/2.md) to specify the desired set of changes to filesystem parameters of the filesystem instance. Once the desired set of changes have been configured, the changes can be effectuated by calling [**fsconfig**(2)](/fsconfig/2.md) with the **FSCONFIG\_CMD\_RECONFIGURE** command. In contrast to the behavior of **MS\_REMOUNT** with [**mount**(2)](/mount/2.md), **fspick**() instantiates the filesystem configuration context with a copy of the extant filesystem's filesystem parameters; thus, subsequent **FSCONFIG\_CMD\_RECONFIGURE** operations will only update filesystem parameters explicitly modified with [**fsconfig**(2)](/fsconfig/2.md). As with "\*at()" system calls, **fspick**() uses the *dirfd* argument in conjunction with the *path* argument to determine the path to operate on, as follows: - • If the pathname given in *path* is absolute, then *dirfd* is ignored. - • If the pathname given in *path* is relative and *dirfd* is the special value **AT\_FDCWD**, then *path* is interpreted relative to the current working directory of the calling process (like [**open**(2)](/open/2.md)). - • If the pathname given in *path* is relative, then it is interpreted relative to the directory referred to by the file descriptor *dirfd* (rather than relative to the current working directory of the calling process, as is done by [**open**(2)](/open/2.md) for a relative pathname). In this case, *dirfd* must be a directory that was opened for reading (**O\_RDONLY**) or using the **O\_PATH** flag. - • If *path* is an empty string, and *flags* contains **FSPICK\_EMPTY\_PATH**, then the file descriptor *dirfd* is operated on directly. In this case, *dirfd* may refer to any type of file, not just a directory. See [**openat**(2)](/openat/2.md) for an explanation of why the *dirfd* argument is useful. *flags* can be used to control aspects of how *path* is resolved and properties of the returned file descriptor. A value for *flags* is constructed by bitwise ORing zero or more of the following constants: - **FSPICK\_CLOEXEC** Set the close-on-exec (**FD\_CLOEXEC**) flag on the new file descriptor. See the description of the **O\_CLOEXEC** flag in [**open**(2)](/open/2.md) for reasons why this may be useful. - **FSPICK\_EMPTY\_PATH** If *path* is an empty string, operate on the file referred to by *dirfd* (which may have been obtained from [**open**(2)](/open/2.md), [**fsmount**(2)](/fsmount/2.md), or [**open\_tree**(2)](/open_tree/2.md)). In this case, *dirfd* may refer to any type of file, not just a directory. If *dirfd* is **AT\_FDCWD**, **fspick**() will operate on the current working directory of the calling process. - **FSPICK\_SYMLINK\_NOFOLLOW** Do not follow symbolic links in the terminal component of *path*. If *path* references a symbolic link, the returned filesystem context will reference the filesystem that the symbolic link itself resides on. - **FSPICK\_NO\_AUTOMOUNT** Do not automount the terminal ("basename") component of *path* if it is a directory that is an automount point. This allows you to reconfigure an automount point, rather than the location that would be mounted. This flag has no effect if the automount point has already been mounted over. As with filesystem contexts created with [**fsopen**(2)](/fsopen/2.md), the file descriptor returned by **fspick**() may be queried for message strings at any time by calling [**read**(2)](/read/2.md) on the file descriptor. (See the "Message retrieval interface" subsection in [**fsopen**(2)](/fsopen/2.md) for more details on the message format.) ## RETURN VALUE On success, a new file descriptor is returned. On error, -1 is returned, and *errno* is set to indicate the error. ## ERRORS - **EACCES** Search permission is denied for one of the directories in the path prefix of *path*. (See also [**path\_resolution**(7)](/path_resolution/7.md).) - **EBADF** *path* is relative but *dirfd* is neither **AT\_FDCWD** nor a valid file descriptor. - **EFAULT** *path* is NULL or a pointer to a location outside the calling process's accessible address space. - **EINVAL** Invalid flag specified in *flags*. - **ELOOP** Too many symbolic links encountered when resolving *path*. - **EMFILE** The calling process has too many open files to create more. - **ENAMETOOLONG** *path* is longer than **PATH\_MAX**. - **ENFILE** The system has too many open files to create more. - **ENOENT** A component of *path* does not exist, or is a dangling symbolic link. - **ENOENT** *path* is an empty string, but **FSPICK\_EMPTY\_PATH** is not specified in *flags*. - **ENOTDIR** A component of the path prefix of *path* is not a directory; or *path* is relative and *dirfd* is a file descriptor referring to a file other than a directory. - **ENOMEM** The kernel could not allocate sufficient memory to complete the operation. - **EPERM** The calling process does not have the required **CAP\_SYS\_ADMIN** capability. ## STANDARDS Linux. ## HISTORY Linux 5.2. glibc 2.36. ## EXAMPLES The following example sets the read-only flag on the filesystem instance referenced by the mount object attached at */tmp*. ``` int fsfd = fspick(AT_FDCWD, "/tmp", FSPICK_CLOEXEC); fsconfig(fsfd, FSCONFIG_SET_FLAG, "ro", NULL, 0); fsconfig(fsfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0); ``` The above procedure is roughly equivalent to the following mount operation using [**mount**(2)](/mount/2.md): ``` mount(NULL, "/tmp", NULL, MS_REMOUNT | MS_RDONLY, NULL); ``` With the notable caveat that in this example, [**mount**(2)](/mount/2.md) will clear all other filesystem parameters (such as **MS\_DIRSYNC** or **MS\_SYNCHRONOUS**); [**fsconfig**(2)](/fsconfig/2.md) will only modify the **ro** parameter. ## SEE ALSO [**fsconfig**(2)](/fsconfig/2.md), [**fsmount**(2)](/fsmount/2.md), [**fsopen**(2)](/fsopen/2.md), [**mount**(2)](/mount/2.md), [**mount\_setattr**(2)](/mount_setattr/2.md), [**move\_mount**(2)](/move_mount/2.md), [**open\_tree**(2)](/open_tree/2.md), [**mount\_namespaces**(7)](/mount_namespaces/7.md)