xfs_quota(8) - phpMan

xfs_quota(8) System Manager's Manual xfs_quota(8)

NAME
xfs_quota - manage use of quota on XFS filesystems

SYNOPSIS
xfs_quota [ -x ] [ -f ] [ -p prog ] [ -c cmd ] ... [ -d project ] ... [ -D projects_file ]
[ -P projid_file ] [ path ... ]
xfs_quota -V

DESCRIPTION
xfs_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 avail-
able only in expert mode.

-f Enable foreign filesystem mode. A limited number of user and administrative
commands are available for use on some foreign (non-XFS) filesystems.

-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.

-D projects_file
Specify a file containing the mapping of numeric project identifiers to direc-
tory trees. /etc/projects as default, if this option is none.

-P projid_file
Specify a file containing the mapping of numeric project identifiers to project
names. /etc/projid as default, if this option is none.

-V Prints the version number and exits.

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 re-
stricted to the set of filesystems specified.

This manual page is divided into two sections - firstly, information for users of filesys-
tems 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.

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 (in-
odes) they can own.

The quota command provides information on the quotas that have been set by the system ad-
ministrators 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 ex-
pected 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 Reached
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 suf-
ficient 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. They can use
the editor shell escape command to examine their file space and remove surplus files. Al-
ternatively, using sh(1), they 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 situ-
ation, the file can be moved back to the filesystem it belongs on.

Default Quotas
The XFS quota subsystem allows a default quota to be enforced for any user, group or
project which does not have a quota limit explicitly set. These limits are stored in and
displayed as ID 0's limits, although they do not actually limit ID 0.

USER COMMANDS
print Lists all paths with devices/project identifiers. The path list can come from sev-
eral places - the command line, the mount table, and the /etc/projects file.

df See the free command.

quota [ -g | -p | -u ] [ -bir ] [ -hnNv ] [ -f file ] [ 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. The -n
option reports the numeric IDs rather than the name. The -N option omits the
header. The -v option outputs verbose information. The -f option sends the output
to file instead of stdout.

free [ -bir ] [ -hN ] [ -f file ]
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 avail-
able. If project quota are in use (see the DIRECTORY TREE QUOTA section below), it
will also report utilisation for those projects (directory trees). The -h option
reports in a "human-readable" format. The -N option omits the header. The -f option
outputs the report to file instead of stdout.

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 im-
portantly, 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 ac-
counting 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 pos-
sible 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 en-
forcement. The "uqnoenforce" option must be used to turn on user accounting with
limit enforcement disabled.

4. Turning on quotas on the root filesystem is slightly different from the above. For
Linux XFS, the quota mount flags must be passed in with the "rootflags=" boot pa-
rameter.

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 oc-
cupied 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
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.

report [ -gpu ] [ -bir ] [ -ahntlLNU ] [ -f file ]
Report filesystem quota information. This reports all quota usage for a filesys-
tem, for the specified quota type (u/g/p and/or blocks/inodes/realtime). It re-
ports blocks in 1KB units by default. The -h option reports in a "human-readable"
format similar to the df(1) command. The -f option outputs the report to file in-
stead of stdout. The -a option reports on all filesystems. By default, outputs the
name of the user/group/project. If no name is defined for a given ID, outputs the
numeric ID instead. The -n option outputs the numeric ID instead of the name. The
-L and -U options specify lower and upper ID bounds to report on. If upper/lower
bounds are specified, then by default only the IDs will be displayed in output;
with the -l option, a lookup will be performed to translate these IDs to names. The
-N option reports information without the header line. The -t option performs a
terse report.

state [ -gpu ] [ -av ] [ -f file ]
Report overall quota state information. This reports on the state of quota ac-
counting, quota enforcement, and the number of extents being used by quota metadata
within the filesystem. The -f option outputs state information to file instead of
stdout. The -a option reports state on all filesystems and not just the current
path.

timer [ -g | -p | -u ] [ -bir ] value [ -d | id | name ]
Allows the quota enforcement timeout (i.e. the amount of time allowed to pass be-
fore the soft limits are enforced as the hard limits) to be modified. The current
timeout setting can be displayed using the state command.
When setting the default timer via the -d option, or for id 0, or if no argument is
given after value the value argument is a number of seconds indicating the relative
amount of time after soft limits are exceeded, before hard limits are enforced.
When setting any other individual timer by id or name, the value is the number of
seconds from now, at which time the hard limits will be enforced. This allows ex-
tending the grace time of an individual user who has exceeded soft limits.
For value, units of 'minutes', 'hours', 'days', and 'weeks' are also understood (as
are their abbreviations 'm', 'h', 'd', and 'w').

warn [ -g | -p | -u ] [ -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 ac-
counting 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 [ -g | -p | -u ] [ -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 [ -g | -p | -u ] [ -f file ]
Restore quota limits from a backup file. The file must be in the format produced
by the dump command.

quot [ -g | -p | -u ] [ -bir ] [ -acnv ] [ -f file ]
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 en-
abled, as it is a full-filesystem scan (it may also take a long time...). The -a
option displays information on all filesystems. The -c option displays a histogram
instead of a report. The -n option displays numeric IDs rather than names. The -v
option displays verbose information. The -f option send the output to file instead
of stdout.

project [ -cCs [ -d depth ] [ -p path ] id | name ]
The -c, -C, and -s options allow the directory tree quota mechanism to be main-
tained. -d allows one to limit recursion level when processing project directories
and -p allows one to specify project paths at command line ( instead of
/etc/projects ). All options are discussed in detail below.

DIRECTORY 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 -s 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.

Option -d can be used to limit recursion level (-1 is infinite, 0 is top level only, 1 is
first level ... ). Option -p adds possibility to specify project paths in command line
without a need for /etc/projects to exist. Note that if projects file exists then it is
also used.

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 -x -c report /home

Enabling project quota on an XFS filesystem (restrict files in log file directories to
only using 1 gigabyte of space).

# mount -o prjquota /dev/xvm/var /var
# echo 42:/var/log >> /etc/projects
# echo logfiles:42 >> /etc/projid
# xfs_quota -x -c 'project -s logfiles' /var
# xfs_quota -x -c 'limit -p bhard=1g logfiles' /var

Same as above without a need for configuration files.

# rm -f /etc/projects /etc/projid
# mount -o prjquota /dev/xvm/var /var
# xfs_quota -x -c 'project -s -p /var/log 42' /var
# xfs_quota -x -c 'limit -p bhard=1g 42' /var

CAVEATS
The XFS allocation mechanism will always reserve the maximum amount of space required be-
fore proceeding with an allocation. If insufficient space for this reservation is avail-
able, due to the block quota limit being reached for example, this may result in the allo-
cation failing even though there is sufficient space. Quota enforcement can thus some-
times happen in situations where the user is under quota and the end result of some opera-
tion 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 func-
tionality on that platform).

FILES
/etc/projects Mapping of numeric project identifiers to directories trees.
/etc/projid Mapping of numeric project identifiers to project names.

SEE ALSO
df(1), mount(1), sync(2), projid(5), projects(5). xfs(5). warnquota(8),

xfs_quota(8)

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