statfs() System Call in Linux

NAME

statfs, fstatfs - get file system statistics

SYNOPSIS

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

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

DESCRIPTION

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 AFFS_SUPER_MAGIC 0xADFF BEFS_SUPER_MAGIC 0x42465331 BFS_MAGIC 0x1BADFACE CIFS_MAGIC_NUMBER 0xFF534D42 CODA_SUPER_MAGIC 0x73757245 COH_SUPER_MAGIC 0x012FF7B7 CRAMFS_MAGIC 0x28cd3d45 DEVFS_SUPER_MAGIC 0x1373 EFS_SUPER_MAGIC 0x00414A53 EXT_SUPER_MAGIC 0x137D EXT2_OLD_SUPER_MAGIC 0xEF51 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 OPENPROM_SUPER_MAGIC 0x9fa1 PROC_SUPER_MAGIC 0x9fa0 QNX4_SUPER_MAGIC 0x002f REISERFS_SUPER_MAGIC 0x52654973 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 USBDEVICE_SUPER_MAGIC 0x9fa2 VXFS_SUPER_MAGIC 0xa501FCF5 XENIX_SUPER_MAGIC 0x012FF7B4 XFS_SUPER_MAGIC 0x58465342 _XIAFS_SUPER_MAGIC 0x012FD16D

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.

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

Tag	Description
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.

CONFORMING TO

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

NOTES

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 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 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 sysfs() system call.