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statfs(2) System Calls Manual statfs(2)


statfs, fstatfs - get filesystem statistics


Standard C library (libc, -lc)


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

Unless you need the f_type field, you should use the standard statvfs(3) interface instead.


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      0xadf5
AFFS_SUPER_MAGIC      0xadff
AFS_SUPER_MAGIC       0x5346414f
ANON_INODE_FS_MAGIC   0x09041934 /* Anonymous inode FS (for

pseudofiles that have no name;
e.g., epoll, signalfd, bpf) */ AUTOFS_SUPER_MAGIC 0x0187 BDEVFS_MAGIC 0x62646576 BEFS_SUPER_MAGIC 0x42465331 BFS_MAGIC 0x1badface BINFMTFS_MAGIC 0x42494e4d BPF_FS_MAGIC 0xcafe4a11 BTRFS_SUPER_MAGIC 0x9123683e BTRFS_TEST_MAGIC 0x73727279 CGROUP_SUPER_MAGIC 0x27e0eb /* Cgroup pseudo FS */ CGROUP2_SUPER_MAGIC 0x63677270 /* Cgroup v2 pseudo FS */ CIFS_MAGIC_NUMBER 0xff534d42 CODA_SUPER_MAGIC 0x73757245 COH_SUPER_MAGIC 0x012ff7b7 CRAMFS_MAGIC 0x28cd3d45 DEBUGFS_MAGIC 0x64626720 DEVFS_SUPER_MAGIC 0x1373 /* Linux 2.6.17 and earlier */ DEVPTS_SUPER_MAGIC 0x1cd1 ECRYPTFS_SUPER_MAGIC 0xf15f EFIVARFS_MAGIC 0xde5e81e4 EFS_SUPER_MAGIC 0x00414a53 EXT_SUPER_MAGIC 0x137d /* Linux 2.0 and earlier */ EXT2_OLD_SUPER_MAGIC 0xef51 EXT2_SUPER_MAGIC 0xef53 EXT3_SUPER_MAGIC 0xef53 EXT4_SUPER_MAGIC 0xef53 F2FS_SUPER_MAGIC 0xf2f52010 FUSE_SUPER_MAGIC 0x65735546 FUTEXFS_SUPER_MAGIC 0xbad1dea /* Unused */ 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 /* 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 0x4d44 MTD_INODE_FS_MAGIC 0x11307854 NCP_SUPER_MAGIC 0x564c NFS_SUPER_MAGIC 0x6969 NILFS_SUPER_MAGIC 0x3434 NSFS_MAGIC 0x6e736673 NTFS_SB_MAGIC 0x5346544e OCFS2_SUPER_MAGIC 0x7461636f OPENPROM_SUPER_MAGIC 0x9fa1 OVERLAYFS_SUPER_MAGIC 0x794c7630 PIPEFS_MAGIC 0x50495045 PROC_SUPER_MAGIC 0x9fa0 /* /proc FS */ PSTOREFS_MAGIC 0x6165676c QNX4_SUPER_MAGIC 0x002f QNX6_SUPER_MAGIC 0x68191122 RAMFS_MAGIC 0x858458f6 REISERFS_SUPER_MAGIC 0x52654973 ROMFS_MAGIC 0x7275 SECURITYFS_MAGIC 0x73636673 SELINUX_MAGIC 0xf97cff8c SMACK_MAGIC 0x43415d53 SMB_SUPER_MAGIC 0x517b SMB2_MAGIC_NUMBER 0xfe534d42 SOCKFS_MAGIC 0x534f434b SQUASHFS_MAGIC 0x73717368 SYSFS_MAGIC 0x62656572 SYSV2_SUPER_MAGIC 0x012ff7b6 SYSV4_SUPER_MAGIC 0x012ff7b5 TMPFS_MAGIC 0x01021994 TRACEFS_MAGIC 0x74726163 UDF_SUPER_MAGIC 0x15013346 UFS_MAGIC 0x00011954 USBDEVICE_SUPER_MAGIC 0x9fa2 V9FS_MAGIC 0x01021997 VXFS_SUPER_MAGIC 0xa501fcf5 XENFS_SUPER_MAGIC 0xabba1974 XENIX_SUPER_MAGIC 0x012ff7b4 XFS_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.


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.




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

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.

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


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.

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.


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)

2024-05-02 Linux man-pages 6.8