int quotactl(int cmd, const char *special, int id, caddr_t addr);
The quota system can be used to set per-user and per-group limits on
the amount of disk space used on a filesystem. For each user and/or
group, a soft limit and a hard limit can be set for each filesystem.
The hard limit can't be exceeded. The soft limit can be exceeded, but
warnings will ensue. Moreover, the user can't exceed the soft limit
for more than one week (by default) at a time; after this time, the
soft limit counts as a hard limit.
The quotactl() call manipulates disk quotas. The cmd argument indi-
cates a command to be applied to the user or group ID specified in id.
To initialize the cmd argument, use the QCMD(subcmd, type) macro. The
type value is either USRQUOTA, for user quotas, or GRPQUOTA, for group
quotas. The subcmd value is described below.
The special argument is a pointer to a null-terminated string contain-
ing the pathname of the (mounted) block special device for the filesys-
tem being manipulated.
The addr argument is the address of an optional, command-specific, data
structure that is copied in or out of the system. The interpretation
of addr is given with each command below.
The subcmd value is one of the following:
Turn on quotas for a filesystem. The id argument is the iden-
tification number of the quota format to be used. Currently,
there are three supported quota formats:
QFMT_VFS_OLD The original quota format.
QFMT_VFS_V0 The standard VFS v0 quota format, which can handle
32-bit UIDs and GIDs and quota limits up to 2^42
bytes and 2^32 inodes.
QFMT_VFS_V1 A quota format that can handle 32-bit UIDs and
GIDs and quota limits of 2^64 bytes and 2^64
The addr argument points to the pathname of a file containing
the quotas for the filesystem. The quota file must exist; it
is normally created with the quotacheck(8) program. This oper-
ation requires privilege (CAP_SYS_ADMIN).
Turn off quotas for a filesystem. The addr and id arguments
are ignored. This operation requires privilege
uint64_t dqb_bsoftlimit; /* preferred limit on
disk quota blocks */
uint64_t dqb_curspace; /* current quota block
uint64_t dqb_ihardlimit; /* maximum number of
allocated inodes */
uint64_t dqb_isoftlimit; /* preferred inode limit */
uint64_t dqb_curinodes; /* current number of
allocated inodes */
uint64_t dqb_btime; /* time limit for excessive
disk use */
uint64_t dqb_itime; /* time limit for excessive
uint32_t dqb_valid; /* bit mask of QIF_*
/* Flags in dqb_valid that indicate which fields in
dqblk structure are valid. */
#define QIF_BLIMITS 1
#define QIF_SPACE 2
#define QIF_ILIMITS 4
#define QIF_INODES 8
#define QIF_BTIME 16
#define QIF_ITIME 32
#define QIF_LIMITS (QIF_BLIMITS | QIF_ILIMITS)
#define QIF_USAGE (QIF_SPACE | QIF_INODES)
#define QIF_TIMES (QIF_BTIME | QIF_ITIME)
#define QIF_ALL (QIF_LIMITS | QIF_USAGE | QIF_TIMES)
The dqb_valid field is a bit mask that is set to indicate the
entries in the dqblk structure that are valid. Currently, the
kernel fills in all entries of the dqblk structure and marks
them as valid in the dqb_valid field. Unprivileged users may
retrieve only their own quotas; a privileged user
(CAP_SYS_ADMIN) can retrieve the quotas of any user.
Set quota information for user or group id, using the informa-
tion supplied in the dqblk structure pointed to by addr. The
dqb_valid field of the dqblk structure indicates which entries
in the structure have been set by the caller. This operation
supersedes the Q_SETQLIM and Q_SETUSE operations in the previ-
ous quota interfaces. This operation requires privilege
Get information (like grace times) about quotafile. The addr
argument should be a pointer to a dqinfo structure. This
structure is defined in <sys/quota.h> as follows:
/* uint64_t is an unsigned 64-bit integer;
uint32_t is an unsigned 32-bit integer */
/* Bits for dqi_flags */
/* Quota format QFMT_VFS_OLD */
#define V1_DQF_RSQUASH 1 /* Root squash enabled */
/* Other quota formats have no dqi_flags bits defined */
/* Flags in dqi_valid that indicate which fields in
dqinfo structure are valid. */
# define IIF_BGRACE 1
# define IIF_IGRACE 2
# define IIF_FLAGS 4
# define IIF_ALL (IIF_BGRACE | IIF_IGRACE | IIF_FLAGS)
The dqi_valid field in the dqinfo structure indicates the
entries in the structure that are valid. Currently, the kernel
fills in all entries of the dqinfo structure and marks them all
as valid in the dqi_valid field. The id argument is ignored.
Set information about quotafile. The addr argument should be a
pointer to a dqinfo structure. The dqi_valid field of the
dqinfo structure indicates the entries in the structure that
have been set by the caller. This operation supersedes the
Q_SETGRACE and Q_SETFLAGS operations in the previous quota
interfaces. The id argument is ignored. This operation
requires privilege (CAP_SYS_ADMIN).
Get quota format used on the specified filesystem. The addr
argument should be a pointer to a 4-byte buffer where the for-
mat number will be stored.
Q_SYNC Update the on-disk copy of quota usages for a filesystem. If
special is NULL, then all filesystems with active quotas are
sync'ed. The addr and id arguments are ignored.
Get statistics and other generic information about the quota
subsystem. The addr argument should be a pointer to a dqstats
structure in which data should be stored. This structure is
defined in <sys/quota.h>. The special and id arguments are
ignored. This operation is obsolete and not supported by
recent kernels. Files in /proc/sys/fs/quota/ carry the infor-
For XFS filesystems making use of the XFS Quota Manager (XQM), the
above commands are bypassed and the following commands are used:
Turn on quotas for an XFS filesystem. XFS provides the ability
to turn on/off quota limit enforcement with quota accounting.
Get disk quota limits and current usage for user id. The addr
argument is a pointer to an fs_disk_quota structure (defined in
<xfs/xqm.h>). Unprivileged users may retrieve only their own
quotas; a privileged user (CAP_SYS_ADMIN) may retrieve the quo-
tas of any user.
Set disk quota limits for user id. The addr argument is a
pointer to an fs_disk_quota structure (defined in <xfs/xqm.h>).
This operation requires privilege (CAP_SYS_ADMIN).
Returns an fs_quota_stat structure containing XFS filesystem-
specific quota information. This is useful for finding out how
much space is used to store quota information, and also to get
quotaon/off status of a given local XFS filesystem.
Free the disk space taken by disk quotas. Quotas must have
already been turned off.
There is no command equivalent to Q_SYNC for XFS since sync(1) writes
quota information to disk (in addition to the other filesystem metadata
that it writes out).
On success, quotactl() returns 0; on error -1 is returned, and errno is
set to indicate the error.
EFAULT addr or special is invalid.
EINVAL cmd or type is invalid.
ENOENT The file specified by special or addr does not exist.
ENOSYS The kernel has not been compiled with the CONFIG_QUOTA option.
special is not a block device.
EPERM The caller lacked the required privilege (CAP_SYS_ADMIN) for the
ESRCH No disk quota is found for the indicated user. Quotas have not
been turned on for this filesystem.
If cmd is Q_SETQUOTA, quotactl() may also set errno to:
ERANGE Specified limits are out of range allowed by quota format.
If cmd is Q_QUOTAON, quotactl() may also set errno to:
quota(1), getrlimit(2), quotacheck(8), quotaon(8)
This page is part of release 4.04 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
Linux 2010-06-16 QUOTACTL(2)
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