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statfs() - Unix, Linux System Call

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statfs, fstatfs - get file system statistics


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

int statfs(const char *path, struct statfs *buf);
int fstatfs(int fd, struct statfs *buf);


The function statfs() returns information about a mounted file system. 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 {
   long    f_type;     /* type of filesystem (see below) */
   long    f_bsize;    /* optimal transfer block size */
   long    f_blocks;   /* total data blocks in file system */
   long    f_bfree;    /* free blocks in fs */
   long    f_bavail;   /* free blocks avail to non-superuser */
   long    f_files;    /* total file nodes in file system */
   long    f_ffree;    /* free file nodes in fs */
   fsid_t  f_fsid;     /* file system id */
   long    f_namelen;  /* maximum length of filenames */

File system types:

   ADFS_SUPER_MAGIC      0xadf5
   BEFS_SUPER_MAGIC      0x42465331
   BFS_MAGIC             0x1BADFACE
   CODA_SUPER_MAGIC      0x73757245
   COH_SUPER_MAGIC       0x012FF7B7
   CRAMFS_MAGIC          0x28cd3d45
   DEVFS_SUPER_MAGIC     0x1373
   EFS_SUPER_MAGIC       0x00414A53
   EXT_SUPER_MAGIC       0x137D
   EXT2_SUPER_MAGIC      0xEF53
   EXT3_SUPER_MAGIC      0xEF53
   HFS_SUPER_MAGIC       0x4244
   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 */
   MSDOS_SUPER_MAGIC     0x4d44
   NCP_SUPER_MAGIC       0x564c
   NFS_SUPER_MAGIC       0x6969
   NTFS_SB_MAGIC         0x5346544e
   PROC_SUPER_MAGIC      0x9fa0
   QNX4_SUPER_MAGIC      0x002f
   ROMFS_MAGIC           0x7275
   SMB_SUPER_MAGIC       0x517B
   SYSV2_SUPER_MAGIC     0x012FF7B6
   SYSV4_SUPER_MAGIC     0x012FF7B5
   TMPFS_MAGIC           0x01021994
   UDF_SUPER_MAGIC       0x15013346
   UFS_MAGIC             0x00011954
   VXFS_SUPER_MAGIC      0xa501FCF5
   XFS_SUPER_MAGIC       0x58465342

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

Fields that are undefined for a particular file system 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.


Error CodeDescription
EACCES (statfs()) Search permission is denied for a component of the path prefix of path. (See also path_resolution(2).)
EBADF (fstatfs()) fd is not a valid open file descriptor.
EFAULT buf or path points to an invalid address.
EINTR This call was interrupted by a signal.
EIO An I/O error occurred while reading from the file system.
ELOOP (statfs()) Too many symbolic links were encountered in translating path.
ENAMETOOLONG (statfs()) path is too long.
ENOENT (statfs()) The file referred to by path does not exist.
ENOMEM Insufficient kernel memory was available.
ENOSYS The file system does not support this call.
ENOTDIR (statfs()) A component of the path prefix of path is not a directory.
EOVERFLOW Some values were too large to be represented in the returned struct.


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


The kernel has system calls statfs(), fstatfs(), statfs64(), and fstatfs64() to support this library call.

Some systems only have <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() and fstatvfs() instead.

The f_fsid field

Solaris, Irix and POSIX have a system callstatvfs(2) that returns astruct 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 OSes use (a variation on) the device number, or the device number combined with the filesystem type. Several OSes 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 OSes the fsid can be used as second parameter to the b>sysfs() system call.


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