.\" Copyright 1996, Andries E. Brouwer <aeb@cwi.nl>
.\" Copyright 2010, Jan Kara <jack@suse.cz>
.\" Copyright 2010, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH Q_QUOTAON 2const 2026-06-05 "Linux man-pages 6.19"
.SH NAME
Q_QUOTAON
\-
turn on quotas for a filesystem
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <sys/quota.h>
.P
.BI "int\~quotactl(QCMD(Q_QUOTAON, " type "), const\~char\~*_Nullable\~" special ,
.BI "             int\~" fmt ", caddr_t\~" quota_path );
.P
.BR "#include <sys/quota.h>" "    /* Definition of " Q_* " constants */"
.BR "#include <sys/syscall.h>" "  /* Definition of " SYS_* " constants */"
.B #include <unistd.h>
.P
.BI "int\~syscall(SYS_quotactl_fd, int\~" fd ", QCMD(Q_QUOTAON, " type ));
.fi
.SH DESCRIPTION
Turn on quotas for a filesystem.
.P
The
.I fmt
argument is the identification number of the quota format to be used.
Currently, there are three supported quota formats:
.TP
.B QFMT_VFS_OLD
The original quota format.
.TP
.B QFMT_VFS_V0
The standard VFS v0 quota format, which can handle 32-bit UIDs and GIDs
and quota limits up to 2\[ha]42 bytes and 2\[ha]32 inodes.
.TP
.B QFMT_VFS_V1
A quota format that can handle 32-bit UIDs and GIDs
and quota limits of 2\[ha]63 \- 1 bytes and 2\[ha]63 \- 1 inodes.
.P
The
.I quota_path
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
.BR quotacheck (8)
program
.P
Quota information can be also stored in hidden system inodes
for ext4, XFS, and other filesystems if the filesystem is configured so.
In this case, there are no visible quota files and there is no need to
use
.BR quotacheck (8).
Quota information is always kept consistent by the filesystem and the
.B Q_QUOTAON
operation serves only to enable enforcement of quota limits.
The presence of hidden
system inodes with quota information is indicated by the
.B DQF_SYS_FILE
flag in the
.I dqi_flags
field returned by the
.BR Q_GETINFO (2const)
operation.
.P
The
.BR quotactl_fd ()
variant of this system call doesn't have the
.I quota_path
and
.I fmt
arguments, so the
.B Q_QUOTAON
operation of
.BR quotactl_fd ()
is only suitable for work with hidden system inodes.
.P
This operation requires privilege
.RB ( CAP_SYS_ADMIN ).
.SH RETURN VALUE
See
.BR quotactl (2).
.SH ERRORS
See
.BR quotactl (2).
.TP
.B EACCES
The quota file pointed to by
.I quota_path
exists, but is not a regular file or
is not on the filesystem pointed to by
.IR special .
.TP
.B EBUSY
Another
.B Q_QUOTAON
had already been performed.
.TP
.B EINVAL
The specified quota file is corrupted.
.TP
.B ESRCH
The specified quota format was not found.
.SH STANDARDS
Linux.
.SH HISTORY
Linux.
.SH SEE ALSO
.BR quotactl (2),
.BR quotactl_fd (2),
.BR Q_QUOTAOFF (2const),
.BR quotacheck (8)