---
name: "maillock"
section: "3"
platform: "linux"
package: "liblockfile"
version: "1.17_2-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/maillock"
---

# maillock(3)

manage mailbox lockfiles

## NAME

maillock, mailunlock, touchlock - manage mailbox lockfiles

## SYNOPSIS

**#include \<maillock.h\>**

**cc \[** *flag* **... \]** *file* **... -llockfile \[** *library* **\]**

**int maillock( const char \****user***, int** *retrycnt* **);**\
 **void mailunlock(** *void* **);**\
 **void touchlock(** *void* **);**

## DESCRIPTION

The **maillock** function tries to create a lockfile for the users mailbox in an NFS-safe (or resistant) way. The algorithm is documented in [**lockfile\_create**(3)](/lockfile_create/3.md)**.**

The mailbox is typically located in **/var/mail.** The name of the lockfile then becomes **/var/mail/USERNAME.lock.** If the environment variable *$MAIL* is set, and it ends with the same username as the username passed to **maillock**(), then that file is taken as the mailbox to lock instead.

There is no good way to see if a lockfile is stale. Therefore if the lockfile is older then 5 minutes, it will be removed. That is why the **touchlock** function is provided: while holding the lock, it needs to be refreshed regulary (every minute or so) by calling **touchlock ()  .**

Finally the **mailunlock** function removes the lockfile.

## RETURN VALUES

**maillock** returns one of the following status codes:

```
   #define L_SUCCESS   0    /* Lockfile created                     */
   #define L_NAMELEN   1    /* Recipient name too long (> 13 chars) */
   #define L_TMPLOCK   2    /* Error creating tmp lockfile          */
   #define L_TMPWRITE  3    /* Can't write pid int tmp lockfile     */
   #define L_MAXTRYS   4    /* Failed after max. number of attempts */
   #define L_ERROR     5    /* Unknown error; check errno           */
   #define L_RMSTALE   8    /* Failed to remove stale lockfile       */
```

## NOTES

These functions are not thread safe. If you need thread safe functions, or you need to lock other mailbox (like) files that are not in the standard location, use [**lockfile\_create**(3)](/lockfile_create/3.md) instead.

These functions call [**lockfile\_create**(3)](/lockfile_create/3.md) to do the work. That function might spawn a set group-id executable to do the actual locking if the current process doesn't have enough priviliges.

There are some issues with flushing the kernels attribute cache if you are using NFS - see the *[lockfile\_create(3)](/lockfile_create/3.md)* manpage.

## FILES

/var/mail/user.lock,\
 /usr/lib/liblockfile.so.1

## AUTHOR

Miquel van Smoorenburg

## SEE ALSO

[**lockfile\_create**(3)](/lockfile_create/3.md), **lockfile\_touch** (3), [**lockfile\_remove**(3)](/lockfile_remove/3.md)