fstatfs(2) get filesystem statistics

Other Alias



#include <sys/vfs.h> /* or <sys/statfs.h> */

int statfs(const char *path, struct statfs *buf);
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 file nodes in filesystem */
    fsfilcnt_t f_ffree;   /* Free file nodes 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 */
Filesystem types:
   ADFS_SUPER_MAGIC      0xadf5
   AFFS_SUPER_MAGIC      0xadff
   BDEVFS_MAGIC          0x62646576
   BEFS_SUPER_MAGIC      0x42465331
   BFS_MAGIC             0x1badface
   BINFMTFS_MAGIC        0x42494e4d
   BTRFS_SUPER_MAGIC     0x9123683e
   CGROUP_SUPER_MAGIC    0x27e0eb
   CIFS_MAGIC_NUMBER     0xff534d42
   CODA_SUPER_MAGIC      0x73757245
   COH_SUPER_MAGIC       0x012ff7b7
   CRAMFS_MAGIC          0x28cd3d45
   DEBUGFS_MAGIC         0x64626720
   DEVFS_SUPER_MAGIC     0x1373
   EFIVARFS_MAGIC        0xde5e81e4
   EFS_SUPER_MAGIC       0x00414a53
   EXT_SUPER_MAGIC       0x137d
   EXT2_SUPER_MAGIC      0xef53
   EXT3_SUPER_MAGIC      0xef53
   EXT4_SUPER_MAGIC      0xef53
   FUSE_SUPER_MAGIC      0x65735546
   FUTEXFS_SUPER_MAGIC   0xbad1dea
   HFS_SUPER_MAGIC       0x4244
   HOSTFS_SUPER_MAGIC    0x00c0ffee
   HPFS_SUPER_MAGIC      0xf995e849
   HUGETLBFS_MAGIC       0x958458f6
   ISOFS_SUPER_MAGIC     0x9660
   JFFS2_SUPER_MAGIC     0x72b6
   JFS_SUPER_MAGIC       0x3153464a
   MINIX_SUPER_MAGIC     0x137f /* orig. minix */
   MINIX_SUPER_MAGIC2    0x138f /* 30 char minix */
   MINIX2_SUPER_MAGIC    0x2468 /* minix V2 */
   MINIX2_SUPER_MAGIC2   0x2478 /* minix V2, 30 char names */
   MINIX3_SUPER_MAGIC    0x4d5a /* minix V3 fs, 60 char names */
   MQUEUE_MAGIC          0x19800202
   MSDOS_SUPER_MAGIC     0x4d44
   NCP_SUPER_MAGIC       0x564c
   NFS_SUPER_MAGIC       0x6969
   NILFS_SUPER_MAGIC     0x3434
   NTFS_SB_MAGIC         0x5346544e
   OCFS2_SUPER_MAGIC     0x7461636f
   PIPEFS_MAGIC          0x50495045
   PROC_SUPER_MAGIC      0x9fa0
   PSTOREFS_MAGIC        0x6165676c
   QNX4_SUPER_MAGIC      0x002f
   QNX6_SUPER_MAGIC      0x68191122
   RAMFS_MAGIC           0x858458f6
   ROMFS_MAGIC           0x7275
   SELINUX_MAGIC         0xf97cff8c
   SMACK_MAGIC           0x43415d53
   SMB_SUPER_MAGIC       0x517b
   SOCKFS_MAGIC          0x534f434b
   SQUASHFS_MAGIC        0x73717368
   SYSFS_MAGIC           0x62656572
   SYSV2_SUPER_MAGIC     0x012ff7b6
   SYSV4_SUPER_MAGIC     0x012ff7b5
   TMPFS_MAGIC           0x01021994
   UDF_SUPER_MAGIC       0x15013346
   UFS_MAGIC             0x00011954
   V9FS_MAGIC            0x01021997
   VXFS_SUPER_MAGIC      0xa501fcf5
   XENFS_SUPER_MAGIC     0xabba1974
   XENIX_SUPER_MAGIC     0x012ff7b4
   XFS_SUPER_MAGIC       0x58465342
   _XIAFS_SUPER_MAGIC    0x012fd16d

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

The f_flags is a bit mask indicating mount options for the file system. 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)).

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 appropriately.


(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.
This 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(2) and fstatvfs(2) instead.

The f_fsid field

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_t f_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).


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