---
name: "logout"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/login/3"
---

# logout(3)

write utmp and wtmp entries

Part of [login(3)](/login/3.md).

## NAME

login, logout - write utmp and wtmp entries

## LIBRARY

System utilities library (*libutil*, *-lutil*)

## SYNOPSIS

```
#include <utmp.h>
```

**void login(const struct utmp \****ut***);** **int logout(const char \****ut\_line***);**

## DESCRIPTION

The *utmp* file records who is currently using the system. The *wtmp* file records all logins and logouts. See [**utmp**(5)](/utmp/5.md).

The function **login**() takes the supplied *struct utmp*, *ut*, and writes it to both the *utmp* and the *wtmp* file.

The function **logout**() clears the entry in the *utmp* file again.

### GNU details

More precisely, **login**() takes the argument *ut* struct, fills the field *ut-\>ut\_type* (if there is such a field) with the value **USER\_PROCESS**, and fills the field *ut-\>ut\_pid* (if there is such a field) with the process ID of the calling process. Then it tries to fill the field *ut-\>ut\_line*. It takes the first of *stdin*, *stdout*, *stderr* that is a terminal, and stores the corresponding pathname minus a possible leading */dev/* into this field, and then writes the struct to the *utmp* file. On the other hand, if no terminal name was found, this field is filled with "???" and the struct is not written to the *utmp* file. After this, the struct is written to the *wtmp* file.

The **logout**() function searches the *utmp* file for an entry matching the *ut\_line* argument. If a record is found, it is updated by zeroing out the *ut\_name* and *ut\_host* fields, updating the *ut\_tv* timestamp field and setting *ut\_type* (if there is such a field) to **DEAD\_PROCESS**.

## RETURN VALUE

The **logout**() function returns 1 if the entry was successfully written to the database, or 0 if an error occurred.

## FILES

- */var/run/utmp*

  user accounting database, configured through **\_PATH\_UTMP** in *\<paths.h\>*

- */var/log/wtmp*

  user accounting log file, configured through **\_PATH\_WTMP** in *\<paths.h\>*

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **login**(), **logout**() | Thread safety | MT-Unsafe race:utent sig:ALRM timer |

In the above table, *utent* in *race:utent* signifies that if any of the functions [**setutent**(3)](/setutent/3.md), [**getutent**(3)](/getutent/3.md), or [**endutent**(3)](/endutent/3.md) are used in parallel in different threads of a program, then data races could occur. **login**() and **logout**() calls those functions, so we use race:utent to remind users.

## VERSIONS

The member *ut\_user* of *struct utmp* is called *ut\_name* in BSD. Therefore, *ut\_name* is defined as an alias for *ut\_user* in *\<utmp.h\>*.

## STANDARDS

BSD.

## SEE ALSO

[**getutent**(3)](/getutent/3.md), [**utmp**(5)](/utmp/5.md)