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fstatfs(2)

statfs(2)System Calls Manualstatfs(2)

statfs, fstatfs - get filesystem statistics

Standard C library (libc, -lc)

#include <sys/vfs.h>    /* or <sys/statfs.h> */
[[deprecated]] int statfs(const char *path, struct statfs *buf);[[deprecated]] int fstatfs(int fd, struct statfs *buf);

The statfs() system call returns information about a mounted filesystem. path is the pathname of any file within the mounted filesystem. buf is a pointer to a statfs structure defined approximately as follows:


struct statfs {
    __fsword_t f_type;    /* Type of filesystem (see below) */
    __fsword_t f_bsize;   /* Optimal transfer block size */
    fsblkcnt_t f_blocks;  /* Total data blocks in filesystem */
    fsblkcnt_t f_bfree;   /* Free blocks in filesystem */
    fsblkcnt_t f_bavail;  /* Free blocks available to
                             unprivileged user */
    fsfilcnt_t f_files;   /* Total inodes in filesystem */
    fsfilcnt_t f_ffree;   /* Free inodes in filesystem */
    fsid_t     f_fsid;    /* Filesystem ID */
    __fsword_t f_namelen; /* Maximum length of filenames */
    __fsword_t f_frsize;  /* Fragment size (since Linux 2.6) */
    __fsword_t f_flags;   /* Mount flags of filesystem
                             (since Linux 2.6.36) */
    __fsword_t f_spare[xxx];
                    /* Padding bytes reserved for future use */};

The following filesystem types may appear in f_type:


ADFS_SUPER_MAGIC      0xadf5AFFS_SUPER_MAGIC      0xadffAFS_SUPER_MAGIC       0x5346414fANON_INODE_FS_MAGIC   0x09041934 /* Anonymous inode FS (for
                                    pseudofiles that have no name;
                                    e.g., epoll, signalfd, bpf) */AUTOFS_SUPER_MAGIC    0x0187BDEVFS_MAGIC          0x62646576BEFS_SUPER_MAGIC      0x42465331BFS_MAGIC             0x1badfaceBINFMTFS_MAGIC        0x42494e4dBPF_FS_MAGIC          0xcafe4a11BTRFS_SUPER_MAGIC     0x9123683eBTRFS_TEST_MAGIC      0x73727279CGROUP_SUPER_MAGIC    0x27e0eb   /* Cgroup pseudo FS */CGROUP2_SUPER_MAGIC   0x63677270 /* Cgroup v2 pseudo FS */CIFS_MAGIC_NUMBER     0xff534d42CODA_SUPER_MAGIC      0x73757245COH_SUPER_MAGIC       0x012ff7b7CRAMFS_MAGIC          0x28cd3d45DEBUGFS_MAGIC         0x64626720DEVFS_SUPER_MAGIC     0x1373     /* Linux 2.6.17 and earlier */DEVPTS_SUPER_MAGIC    0x1cd1ECRYPTFS_SUPER_MAGIC  0xf15fEFIVARFS_MAGIC        0xde5e81e4EFS_SUPER_MAGIC       0x00414a53EXT_SUPER_MAGIC       0x137d     /* Linux 2.0 and earlier */EXT2_OLD_SUPER_MAGIC  0xef51EXT2_SUPER_MAGIC      0xef53EXT3_SUPER_MAGIC      0xef53EXT4_SUPER_MAGIC      0xef53F2FS_SUPER_MAGIC      0xf2f52010FUSE_SUPER_MAGIC      0x65735546FUTEXFS_SUPER_MAGIC   0xbad1dea  /* Unused */HFS_SUPER_MAGIC       0x4244HOSTFS_SUPER_MAGIC    0x00c0ffeeHPFS_SUPER_MAGIC      0xf995e849HUGETLBFS_MAGIC       0x958458f6ISOFS_SUPER_MAGIC     0x9660JFFS2_SUPER_MAGIC     0x72b6JFS_SUPER_MAGIC       0x3153464aMINIX_SUPER_MAGIC     0x137f     /* original minix FS */MINIX_SUPER_MAGIC2    0x138f     /* 30 char minix FS */MINIX2_SUPER_MAGIC    0x2468     /* minix V2 FS */MINIX2_SUPER_MAGIC2   0x2478     /* minix V2 FS, 30 char names */MINIX3_SUPER_MAGIC    0x4d5a     /* minix V3 FS, 60 char names */MQUEUE_MAGIC          0x19800202 /* POSIX message queue FS */MSDOS_SUPER_MAGIC     0x4d44MTD_INODE_FS_MAGIC    0x11307854NCP_SUPER_MAGIC       0x564cNFS_SUPER_MAGIC       0x6969NILFS_SUPER_MAGIC     0x3434NSFS_MAGIC            0x6e736673NTFS_SB_MAGIC         0x5346544eOCFS2_SUPER_MAGIC     0x7461636fOPENPROM_SUPER_MAGIC  0x9fa1OVERLAYFS_SUPER_MAGIC 0x794c7630PIPEFS_MAGIC          0x50495045PROC_SUPER_MAGIC      0x9fa0     /* /proc FS */PSTOREFS_MAGIC        0x6165676cQNX4_SUPER_MAGIC      0x002fQNX6_SUPER_MAGIC      0x68191122RAMFS_MAGIC           0x858458f6REISERFS_SUPER_MAGIC  0x52654973ROMFS_MAGIC           0x7275SECURITYFS_MAGIC      0x73636673SELINUX_MAGIC         0xf97cff8cSMACK_MAGIC           0x43415d53SMB_SUPER_MAGIC       0x517bSMB2_MAGIC_NUMBER     0xfe534d42SOCKFS_MAGIC          0x534f434bSQUASHFS_MAGIC        0x73717368SYSFS_MAGIC           0x62656572SYSV2_SUPER_MAGIC     0x012ff7b6SYSV4_SUPER_MAGIC     0x012ff7b5TMPFS_MAGIC           0x01021994TRACEFS_MAGIC         0x74726163UDF_SUPER_MAGIC       0x15013346UFS_MAGIC             0x00011954USBDEVICE_SUPER_MAGIC 0x9fa2V9FS_MAGIC            0x01021997VXFS_SUPER_MAGIC      0xa501fcf5XENFS_SUPER_MAGIC     0xabba1974XENIX_SUPER_MAGIC     0x012ff7b4XFS_SUPER_MAGIC       0x58465342_XIAFS_SUPER_MAGIC    0x012fd16d /* Linux 2.0 and earlier */

Most of these MAGIC constants are defined in /usr/include/linux/magic.h, and some are hardcoded in kernel sources.

The f_flags field is a bit mask indicating mount options for the filesystem. It contains zero or more of the following bits:

Mandatory locking is permitted on the filesystem (see fcntl(2)).
Do not update access times; see mount(2).
Disallow access to device special files on this filesystem.
Do not update directory access times; see mount(2).
Execution of programs is disallowed on this filesystem.
The set-user-ID and set-group-ID bits are ignored by exec(3) for executable files on this filesystem
This filesystem is mounted read-only.
Update atime relative to mtime/ctime; see mount(2).
Writes are synched to the filesystem immediately (see the description of O_SYNC in open(2)).
Symbolic links are not followed when resolving paths; see mount(2).

Nobody knows what f_fsid is supposed to contain (but see below).

Fields that are undefined for a particular filesystem are set to 0.

fstatfs() returns the same information about an open file referenced by descriptor fd.

On success, zero is returned. On error, -1 is returned, and errno is set to indicate the error.

(statfs()) Search permission is denied for a component of the path prefix of path. (See also path_resolution(7).)
(fstatfs()) fd is not a valid open file descriptor.
buf or path points to an invalid address.
The call was interrupted by a signal; see signal(7).
An I/O error occurred while reading from the filesystem.
(statfs()) Too many symbolic links were encountered in translating path.
(statfs()) path is too long.
(statfs()) The file referred to by path does not exist.
Insufficient kernel memory was available.
The filesystem does not support this call.
(statfs()) A component of the path prefix of path is not a directory.
Some values were too large to be represented in the returned struct.

Linux-specific. The Linux statfs() was inspired by the 4.4BSD one (but they do not use the same structure).

The __fsword_t type used for various fields in the statfs structure definition is a glibc internal type, not intended for public use. This leaves the programmer in a bit of a conundrum when trying to copy or compare these fields to local variables in a program. Using unsigned int for such variables suffices on most systems.

The original Linux statfs() and fstatfs() system calls were not designed with extremely large file sizes in mind. Subsequently, Linux 2.6 added new statfs64() and fstatfs64() system calls that employ a new structure, statfs64. The new structure contains the same fields as the original statfs structure, but the sizes of various fields are increased, to accommodate large file sizes. The glibc statfs() and fstatfs() wrapper functions transparently deal with the kernel differences.

Some systems have only <sys/vfs.h>, other systems also have <sys/statfs.h>, where the former includes the latter. So it seems including the former is the best choice.

LSB has deprecated the library calls statfs() and fstatfs() and tells us to use statvfs(3) and fstatvfs(3) instead.

Solaris, Irix, and POSIX have a system call statvfs(2) that returns a struct statvfs (defined in <sys/statvfs.h>) containing an unsigned long f_fsid. Linux, SunOS, HP-UX, 4.4BSD have a system call statfs() that returns a struct statfs (defined in <sys/vfs.h>) containing a fsid_tf_fsid, where fsid_t is defined as struct { int val[2]; }. The same holds for FreeBSD, except that it uses the include file <sys/mount.h>.

The general idea is that f_fsid contains some random stuff such that the pair (f_fsid,ino) uniquely determines a file. Some operating systems use (a variation on) the device number, or the device number combined with the filesystem type. Several operating systems restrict giving out the f_fsid field to the superuser only (and zero it for unprivileged users), because this field is used in the filehandle of the filesystem when NFS-exported, and giving it out is a security concern.

Under some operating systems, the fsid can be used as the second argument to the sysfs(2) system call.

From Linux 2.6.38 up to and including Linux 3.1, fstatfs() failed with the error ENOSYS for file descriptors created by pipe(2).

stat(2), statvfs(3), path_resolution(7)

2022-10-30Linux man-pages 6.03