This ioctl() call manipulates disk quotas. fd is the file descriptor returned by the open() system call after opening the quotas file (located in the root directory of the filesystem running quotas.) Q_QUOTACTL is defined in /usr/include/sys/fs/ufs_quota.h. qp is the address of the quotctl structure which is defined as

struct quotctl {
  int op;
  uid_t uid;
  caddr_t addr;
};

op indicates an operation to be applied to the user ID uid. (See below.) addr is the address of an optional, command specific, data structure which is copied in or out of the system. The interpretation of addr is given with each value of op below.

Q_QUOTAON

Turn on quotas for a file system. addr points to the full pathname of the quotas file. uid is ignored. It is recommended that uid have the value of 0. This call is restricted to the super-user.

Q_QUOTAOFF

Turn off quotas for a file system. addr and uid are ignored. It is recommended that addr have the value of NULL and uid have the value of 0. This call is restricted to the super-user.

Q_GETQUOTA

Get disk quota limits and current usage for user uid. addr is a pointer to a dqblk structure (defined in <sys/fs/ufs_quota.h>). Only the super-user may get the quotas of a user other than himself.

Q_SETQUOTA

Set disk quota limits and current usage for user uid. addr is a pointer to a dqblk structure (defined in sys/fs/ufs_quota.h). This call is restricted to the super-user.

Q_SETQLIM

Set disk quota limits for user uid. addr is a pointer to a dqblk structure (defined in sys/fs/ufs_quota.h). This call is restricted to the super-user.

Q_SYNC

Update the on-disk copy of quota usages for this file system. addr and uid are ignored.

Q_ALLSYNC

Update the on-disk copy of quota usages for all file systems with active quotas. addr and uid are ignored.

This ioctl() returns:

0

on success.

-1

on failure and sets errno to indicate the error.

EFAULT

addr is invalid.

EINVAL

The kernel has not been compiled with the QUOTA option. op is invalid.

ENOENT

The quotas file specified by addr does not exist.

EPERM

The call is privileged and the caller was not the super-user.

ESRCH

No disk quota is found for the indicated user. Quotas have not been turned on for this file system.

EUSERS

The quota table is full.

If op is Q_QUOTAON, ioctl() may set errno to:

EACCES

The quota file pointed to by addr exists but is not a regular file. The quota file pointed to by addr exists but is not on the file system pointed to by special.

EIO

Internal I/O error while attempting to read the quotas file pointed to by addr.

/usr/include/sys/fs/ufs_quota.h

quota-related structure/function definitions and defines

quota(1M), quotacheck(1M), quotaon(1M), getrlimit(2), mount(2)

There should be some way to integrate this call with the resource limit interface provided by setrlimit() and getrlimit(2).

This call is incompatible with Melbourne quotas.