QUOTACTL(2)

💖 QUOTACTL(2) — the file system quota whisperer 💖

okay so bestie, this is a section 2 page from the System Calls Manual, and we're talking about quotactl — the syscall that runs your file system quotas. enabling them, disabling them, reading them, writing them. it's giving backstage-pass-to-the-quota-table energy. 🎀

---

🌸 NAME 🌸

quotactl — manipulate file system quotas

📚 LIBRARY 📚

Standard C Library (libc, -lc)

✨ SYNOPSIS ✨

#include <sys/types.h>
#include <ufs/ufs/quota.h>

int
quotactl(const char *path, int cmd, int id, void *addr);

🦋 DESCRIPTION 🦋

The quotactl() system call enables, disables and manipulates file system quotas. A quota control command given by cmd operates on the given filename path for the given user or group id.

(NOTE: One should use the QCMD macro defined in <ufs/ufs/quota.h> to formulate the value for cmd.) — this is not optional advice, bestie, this is the way. don't hand-roll your cmd values. 💅

The address of an optional command specific data structure, addr, may be given; its interpretation is discussed below with each command.

For commands that use the id identifier, it must be either -1 or any positive value. The value of -1 indicates that the current UID or GID should be used. Any other negative value will return an error. (so like. -2? -500? no ma'am. error. 🚫)

Currently quotas are supported only for the "ufs" file system. For "ufs", a command is composed of a primary command (see below) and a command type used to interpret the id. Types are supported for interpretation of user identifiers (USRQUOTA) and group identifiers (GRPQUOTA).

The "ufs" specific commands are:

• Q_QUOTAON — Enable disk quotas for the file system specified by path. The command type specifies the type of the quotas being enabled. The addr argument specifies a file from which to take the quotas. The quota file must exist; it is normally created with the quotacheck(8) program. The id argument is unused. Only the super-user may turn quotas on. 👑
• Q_QUOTAOFF — Disable disk quotas for the file system specified by path. The command type specifies the type of the quotas being disabled. The addr and id arguments are unused. Only the super-user may turn quotas off. 👑
• Q_GETQUOTASIZE — Get the wordsize used to represent the quotas for the user or group (as determined by the command type). Possible values are 32 for the old-style quota file and 64 for the new-style quota file. The addr argument is a pointer to an integer into which the size is stored. The identifier id is not used.
• Q_GETQUOTA — Get disk quota limits and current usage for the user or group (as determined by the command type) with identifier id. The addr argument is a pointer to a struct dqblk structure (defined in <ufs/ufs/quota.h>).
• Q_SETQUOTA — Set disk quota limits for the user or group (as determined by the command type) with identifier id. The addr argument is a pointer to a struct dqblk structure (defined in <ufs/ufs/quota.h>). The usage fields of the dqblk structure are ignored. This system call is restricted to the super-user. 👑
• Q_SETUSE — Set disk usage limits for the user or group (as determined by the command type) with identifier id. The addr argument is a pointer to a struct dqblk structure (defined in <ufs/ufs/quota.h>). Only the usage fields are used. This system call is restricted to the super-user. 👑
• Q_SYNC — Update the on-disk copy of quota usages. The command type specifies which type of quotas are to be updated. The id and addr arguments are ignored.

---

🫶 RETURN VALUES 🫶

The quotactl() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

zero means slay. negative one means check errno, bestie. 😭

---

💀 ERRORS 💀

The quotactl() system call will fail if:

• [EOPNOTSUPP] — The kernel has not been compiled with the QUOTA option. (you literally cannot, it's not in there 🚫)
• [EUSERS] — The quota table cannot be expanded.
• [EINVAL] — The cmd argument or the command type is invalid. In Q_GETQUOTASIZE, Q_GETQUOTA, Q_SETQUOTA, and Q_SETUSE, quotas are not currently enabled for this file system.
  • The id argument to Q_GETQUOTA, Q_SETQUOTA or Q_SETUSE is a negative value.
• [EACCES] — In Q_QUOTAON, the quota file is not a plain file.
• [EACCES] — Search permission is denied for a component of a path prefix.
• [ENOTDIR] — A component of a path prefix was not a directory.
• [ENAMETOOLONG] — A component of either pathname exceeded 255 characters, or the entire length of either path name exceeded 1023 characters.
• [ENOENT] — A filename does not exist.
• [ELOOP] — Too many symbolic links were encountered in translating a pathname.
• [EROFS] — In Q_QUOTAON, either the file system on which quotas are to be enabled is mounted read-only or the quota file resides on a read-only file system.
• [EIO] — An I/O error occurred while reading from or writing to a file containing quotas.
• [EINTEGRITY] — Corrupted data was detected while reading from the file system.
• [EFAULT] — An invalid addr was supplied; the associated structure could not be copied in or out of the kernel.
• [EFAULT] — The path argument points outside the process's allocated address space.
• [EPERM] — The call was privileged and the caller was not the super-user.

heads up: two of these are literally the same errno (EFAULT) for two different reasons, and that's just how it is. not me being confused, that's the actual page. 🙈

---

👀 SEE ALSO 👀

quota(1), fstab(5), edquota(8), quotacheck(8), quotaon(8), repquota(8)

---

🌈 HISTORY 🌈

The quotactl() system call appeared in 4.3BSD-Reno. vintage. iconic. 👑

---

🍓 BUGS 🍓

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

---

okay that's the whole page, bestie. this beauty came out of Debian, dated March 30, 2020 — go forth and quota responsibly, and remember: super-user only for the turning-on-and-off parts. 💜✨🎀