xfs_quota(1M)xfs_quota(1M)NAMExfs_quota - manage use of quota on XFS filesystems
SYNOPSISxfs_quota [ -x ] [ -p prog ] [ -c cmd ] ...
[ -d project ] ... [path...]
DESCRIPTIONxfs_quota is a utility for reporting and editing various aspects of
filesystem quota.
The options to xfs_quota are:
-c cmd xfs_quota commands may be run interactively (the default) or as
arguments on the command line. Multiple -c arguments may be
given. The commands are run in the sequence given, then the
program exits.
-p prog Set the program name for prompts and some error messages, the
default value is xfs_quota.
-x Enable expert mode. All of the administrative commands (see
the ADMINISTRATOR COMMANDS section below) which allow
modifications to the quota system are available only in expert
mode.
-d project
Project names or numeric identifiers may be specified with this
option, which restricts the output of the individual xfs_quota
commands to the set of projects specified. Multiple -d
arguments may be given.
The optional path argument(s) can be used to specify mount points or
device files which identify XFS filesystems. The output of the
individual xfs_quota commands will then be restricted to the set of
filesystems specified.
This manual page is divided into two sections - firstly, information for
users of filesystems with quota enabled, and the xfs_quota commands of
interest to such users; and then information which is useful only to
administrators of XFS filesystems using quota and the quota commands
which allow modifications to the quota system.
Note that common to almost all of the individual commands described below
are the options for specifying which quota types are of interest - user
quota (-u), group quota (-g), and/or project quota (-p). Also, several
commands provide options to operate on "blocks used" (-b), "inodes used"
(-i), and/or "realtime blocks used" (-r).
Many commands also have extensive online help. Use the help command for
more details on any command.
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xfs_quota(1M)xfs_quota(1M)QUOTA OVERVIEW
In most computing environments, disk space is not infinite. The quota
subsystem provides a mechanism to control usage of disk space. Quotas
can be set for each individual user on any/all of the local filesystems.
The quota subsystem warns users when they exceed their allotted limit,
but allows some extra space for current work (hard limit/soft limit). In
addition, XFS filesystems with limit enforcement turned off can be used
as an effective disk usage accounting system.
Users' View of Disk Quotas
To most users, disk quotas are either of no concern or a fact of life
that cannot be avoided. There are two possible quotas that can be
imposed - a limit can be set on the amount of space a user can occupy,
and there may be a limit on the number of files (inodes) he can own.
The quota command provides information on the quotas that have been set
by the system administrators and current usage.
There are four numbers for each limit: current usage, soft limit
(quota), hard limit, and time limit. The soft limit is the number of
1K-blocks (or files) that the user is expected to remain below. The hard
limit cannot be exceeded. If a user's usage reaches the hard limit,
further requests for space (or attempts to create a file) fail with the
"Quota exceeded" (EDQUOT) error.
When a user exceeds the soft limit, the timer is enabled. Any time the
quota drops below the soft limits, the timer is disabled. If the timer
pops, the particular limit that has been exceeded is treated as if the
hard limit has been reached, and no more resources are allocated to the
user. The only way to reset this condition, short of turning off limit
enforcement or increasing the limit, is to reduce usage below quota.
Only the superuser (i.e. a sufficiently capable process) can set the time
limits and this is done on a per filesystem basis.
Surviving When the Quota Limit Is
In most cases, the only way for a user to recover from over-quota
conditions is to abort whatever activity is in progress on the filesystem
that has reached its limit, remove sufficient files to bring the limit
back below quota, and retry the failed program.
However, if a user is in the editor and a write fails because of an over
quota situation, that is not a suitable course of action. It is most
likely that initially attempting to write the file has truncated its
previous contents, so if the editor is aborted without correctly writing
the file, not only are the recent changes lost, but possibly much, or
even all, of the contents that previously existed.
There are several possible safe exits for a user caught in this
situation. He can use the editor shell escape command to examine his
file space and remove surplus files. Alternatively, using sh(1), he can
suspend the editor, remove some files, then resume it. A third
possibility is to write the file to some other filesystem (perhaps to a
file on /tmp) where the user's quota has not been exceeded. Then after
rectifying the quota situation, the file can be moved back to the
filesystem it belongs on.
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xfs_quota(1M)xfs_quota(1M)USER COMMANDS
path [ N ]
Lists all paths with devices/project identifiers or set the current
path to the Nth list entry (the current path is used by many of the
commands described here, it identifies the filesystem toward which a
command is directed). The path list can come from several places -
the command line, the mount table, and the /etc/projects file.
df See the free command.
quota [ -gpu ] [ -bir ] [ -hnNv ] [ id|name ] ...
Show individual usage and limits, for a single user name or numeric
user ID. The -h option reports in a "human-readable" format similar
to the df(1) command.
free [ -bir ] [ -hN ]
Reports filesystem usage, much like the df(1) utility. It can show
usage for blocks, inode, and/or realtime block space, and shows
used, free, and total available. If directory quota are in use (see
the DIRECTORY QUOTA section below), it will also report utilisation
for those directory trees. The -h option reports in a "human-
readable" format,
help [ command]
Online help for all commands, or one specific command.
quit Exit xfs_quota.
q See the quit command.
QUOTA ADMINISTRATION
The XFS quota system differs to that of other filesystems in a number of
ways. Most importantly, XFS considers quota information as filesystem
metadata and uses journaling to provide a higher level guarantee of
consistency. As such, it is administered differently, in particular:
1. The quotacheck command has no effect on XFS filesystems. The first
time quota accounting is turned on (at mount time), XFS does an
automatic quotacheck internally; afterwards, the quota system will
always be completely consistent until quotas are manually turned
off.
2. There is no need for quota file(s) in the root of the XFS
filesystem.
3. XFS distinguishes between quota accounting and limit enforcement.
Quota accounting must be turned on at the time of mounting the XFS
filesystem. However, it is possible to turn on/off limit
enforcement any time quota accounting is turned on. The "quota"
option to the mount command turns on both (user) quota accounting
and enforcement. The "uqnoenforce" option must be used to turn on
user accounting with limit enforcement disabled.
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xfs_quota(1M)xfs_quota(1M)
4. Turning on quotas on the root filesystem is slightly different from
the above. For IRIX XFS, refer to quotaon(1M). For Linux XFS, the
quota mount flags must be passed in with the "rootflags=" boot
parameter.
5. It is useful to use the state to monitor the XFS quota subsystem at
various stages - it can be used to see if quotas are turned on, and
also to monitor the space occupied by the quota system itself..
6. There is a mechanism built into xfsdump that allows quota limit
information to be backed up for later restoration, should the need
arise.
7. Quota limits cannot be set before turning on quotas on.
8. XFS filesystems keep quota accounting on the superuser (user ID
zero), and the tool will display the superuser's usage information.
However, limits are never enforced on the superuser (nor are they
enforced for group and project ID zero).
9. XFS filesystems perform quota accounting whether the user has quota
limits or not.
10. XFS supports the notion of project quota, which can be used to
implement a form of directory tree quota (i.e. to restrict a
directory tree to only being able to use up a component of the
filesystems available space; or simply to keep track of the amount
of space used, or number of inodes, within the tree).
ADMINISTRATOR COMMANDS
report [ -gpu ] [ -bir ] [ -ahnNt ]
Report filesystem quota information. This reports all quota usage
for a filesystem, for the specified quota type (u/g/p and/or
blocks/inodes/realtime). It reports blocks in 1KB units by default.
The -h option reports in a "human-readable" format similar to the
df(1) command.
state [ -gpu ]
Report overall quota state information. This reports on the state
of quota accounting, quota enforcement, and the number of extents
being used by quota metadata within the filesystem.
limit [ -gpu ] .br bsoft=N | bhard=N | isoft=N | ihard=N | rtbsoft=N |
rtbhard=N... -d|id|name
Set quota block limits (bhard/bsoft), inode count limits
(ihard/isoft) and/or realtime block limits (rtbhard/rtbsoft). The
-d option (defaults) can be used to set the default value that will
be used, otherwise a specific user/group/project name or numeric
identifier must be specified.
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xfs_quota(1M)xfs_quota(1M)
timer [ -gpu ] [ -bir ] value
Allows the quota enforcement timeout (i.e. the amount of time
allowed to pass before the soft limits are enforced as the hard
limits) to be modified. The current timeout setting can be
displayed using the state command. The value argument is a number
of seconds, but units of 'seconds', (as are their abbreviations,
's', 'm', 'h', 'd', and 'w').
warn [ -gpu ] [ -bir ] value -d|id|name
Allows the quota warnings limit (i.e. the number of times a warning
will be send to someone over quota) to be viewed and modified. The
-d option (defaults) can be used to set the default time that will
be used, otherwise a specific user/group/project name or numeric
identifier must be specified. NOTE: this feature is not currently
implemented.
enable [ -gpu ] [ -v ]
Switches on quota enforcement for the filesystem identified by the
current path. This requires the filesystem to have been mounted
with quota enabled, and for accounting to be currently active. The
-v option (verbose) displays the state after the operation has
completed.
disable [ -gpu ] [ -v ]
Disables quota enforcement, while leaving quota accounting active.
The -v option (verbose) displays the state after the operation has
completed.
off [ -gpu ] [ -v ]
Permanently switches quota off for the filesystem identified by the
current path. Quota can only be switched back on subsequently by
unmounting and then mounting again.
remove [ -gpu ] [ -v ]
Remove any space allocated to quota metadata from the filesystem
identified by the current path. Quota must not be enabled on the
filesystem, else this operation will report an error.
dump [ -gpu ] [ -f file ]
Dump out quota limit information for backup utilities, either to
standard output (default) or to a file. This is only the limits,
not the usage information, of course.
restore [ -gpu ] [ -f file ]
Restore quota limits from a backup file. The file must be in the
format produced by the dump command.
quot [ -gpu ] [ -bir ] [ -av ] [ -c ]
Summarize filesystem ownership, by user, group or project. This
command uses a special XFS "bulkstat" interface to quickly scan an
entire filesystem and report usage information. This command can be
used even when filesystem quota are not enabled, as it is a full-
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filesystem scan (it may also take a long time...).
project [ -cds id|name ]
Without arguments, this command lists known project names and
identifiers (based on entries in the /etc/projects and /etc/projid
files). The -c, -C, and -s options allow the directory tree quota
mechanism, discussed in detail below, to be maintained.
TREE QUOTA
The project quota mechanism in XFS can be used to implement a form of
directory tree quota, where a specified directory and all of the files
and subdirectories below it (i.e. a tree) can be restricted to using a
subset of the available space in the filesystem.
A managed tree must be setup initially using the -c option to the project
command. The specified project name or identifier is matched to one or
more trees defined in /etc/projects, and these trees are then recursively
descended to mark the affected inodes as being part of that tree. This
process sets an inode flag and the project identifier on every file in
the affected tree. Once this has been done, new files created in the
tree will automatically be accounted to the tree based on their project
identifier. An attempt to create a hard link to a file in the tree will
only succeed if the project identifier matches the project identifier for
the tree. The xfs_io utility can be used to set the project ID for an
arbitrary file, but this can only be done by a privileged user.
A previously setup tree can be cleared from project quota control through
use of the project -C option, which will recursively descend the tree,
clearing the affected inodes from project quota control.
Finally, the project -c option can be used to check whether a tree is
setup, it reports nothing if the tree is correct, otherwise it reports
the paths of inodes which do not have the project ID of the rest of the
tree, or if the inode flag is not set.
FILE FORMATS
There are two files involved with the tree quota mechanism, namely
/etc/projects and /etc/projid. The latter is optional. The projects
file provides a mapping between numeric project identifiers and those
directories which are the roots of the quota tree. Its format is simply:
# comments are hash-prefixed
# ...
10:/export/cage
42:/var/log
The projid file provides a mapping between numeric project identifiers
and a simple human readable name (similar relationship to the one that
exists between usernames and uids). Its format is simply:
# comments are hash-prefixed
# ...
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10:cage
42:logfiles
This file is optional, if a project identifier cannot be mapped to a
name, it will be displayed as a number only.
EXAMPLES
Enabling quota enforcement on an XFS filesystem (restrict a user to a set
amount of space).
# mount -o uquota /dev/xvm/home /home
# xfs_quota-x -c 'limit bsoft=500m bhard=550m tanya' /home
# xfs_quota-c report /home
Enabling directory quota on an XFS filesystem (restrict files in log file
directories to only using 1 gigabyte of space).
# mount -o pquota /dev/xvm/var /var
# echo 42:/var/log >> /etc/projects
# echo logfiles:42 >> /etc/projid
# xfs_quota-x -c 'projects -c logfiles' /home
# xfs_quota-x -c 'limit -p bhard=1g logfiles' /home
CAVEATS
XFS implements delayed allocation (aka. allocate-on-flush) and this has
implications for the quota subsystem. Since quota accounting can only be
done when blocks are actually allocated, it is possible to issue
(buffered) writes into a file and not see the usage immediately updated.
Only when the data is actually written out, either via one of the kernels
flushing mechanisms, or via a manual sync(2), will the usage reported
reflect what has actually been written.
In addition, the XFS allocation mechanism will always reserve the maximum
amount of space required before proceeding with an allocation. If
insufficient space for this reservation is available, due to the block
quota limit being reached for example, this may result in the allocation
failing even though there is sufficient space. Quota enforcement can
thus sometimes happen in situations where the user is under quota and the
end result of some operation would still have left the user under quota
had the operation been allowed to run its course. This additional
overhead is typically in the range of tens of blocks.
Both of these properties are unavoidable side effects of the way XFS
operates, so should be kept in mind when assigning block limits.
BUGS
Quota support for filesystems with realtime subvolumes is not yet
implemented, nor is the quota warning mechanism (the Linux warnquota(8)
tool can be used to provide similar functionality on that platform).
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xfs_quota(1M)xfs_quota(1M)FILES
/etc/projects Mapping of numeric project identifiers to directories
trees.
/etc/projid Mapping of numeric project identifiers to project
names.
IRIX SEE ALSOquotaon(1M), xfs(4).
LINUX SEE ALSOwarnquota(8), xfs(5).
SEE ALSOdf(1), mount(1), sync(2),
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