---
name: "sys_types.h"
section: "0p"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/sys_types.h"
---

# sys\_types.h(0p)

data types

## PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

## NAME

sys/types.h — data types

## SYNOPSIS

```
#include <sys/types.h>
```

## DESCRIPTION

The *\<sys/types.h\>* header shall define at least the following types:

- **blkcnt\_t**

  Used for file block counts.

- **blksize\_t**

  Used for block sizes.

- **clock\_t**

  Used for system times in clock ticks or CLOCKS\_PER\_SEC; see *\<time.h\>*.

- **clockid\_t**

  Used for clock ID type in the clock and timer functions.

- **dev\_t**

  Used for device IDs.

- **fsblkcnt\_t**

  Used for file system block counts.

- **fsfilcnt\_t**

  Used for file system file counts.

- **gid\_t**

  Used for group IDs.

- **id\_t**

  Used as a general identifier; can be used to contain at least a **pid\_t**, **uid\_t**, or **gid\_t**.

- **ino\_t**

  Used for file serial numbers.

- **key\_t**

  Used for XSI interprocess communication.

- **mode\_t**

  Used for some file attributes.

- **nlink\_t**

  Used for link counts.

- **off\_t**

  Used for file sizes.

- **pid\_t**

  Used for process IDs and process group IDs.

- **pthread\_attr\_t**

  Used to identify a thread attribute object.

- **pthread\_barrier\_t**

  Used to identify a barrier.

- **pthread\_barrierattr\_t**

  Used to define a barrier attributes object.

- **pthread\_cond\_t**

  Used for condition variables.

- **pthread\_condattr\_t**

  Used to identify a condition attribute object.

- **pthread\_key\_t**

  Used for thread-specific data keys.

- **pthread\_mutex\_t**

  Used for mutexes.

- **pthread\_mutexattr\_t**

  Used to identify a mutex attribute object.

- **pthread\_once\_t**

  Used for dynamic package initialization.

- **pthread\_rwlock\_t**

  Used for read-write locks.

- **pthread\_rwlockattr\_t**

  Used for read-write lock attributes.

- **pthread\_spinlock\_t**

  Used to identify a spin lock.

- **pthread\_t**

  Used to identify a thread.

- **size\_t**

  Used for sizes of objects.

- **ssize\_t**

  Used for a count of bytes or an error indication.

- **suseconds\_t**

  Used for time in microseconds.

- **time\_t**

  Used for time in seconds.

- **timer\_t**

  Used for timer ID returned by *timer\_create*().

- **trace\_attr\_t**

  Used to identify a trace stream attributes object

- **trace\_event\_id\_t**

  Used to identify a trace event type.

- **trace\_event\_set\_t**

  Used to identify a trace event type set.

- **trace\_id\_t**

  Used to identify a trace stream.

- **uid\_t**

  Used for user IDs.

All of the types shall be defined as arithmetic types of an appropriate length, with the following exceptions:

```
pthread_attr_t
pthread_barrier_t
pthread_barrierattr_t
pthread_cond_t
pthread_condattr_t
pthread_key_t
pthread_mutex_t
pthread_mutexattr_t
pthread_once_t
pthread_rwlock_t
pthread_rwlockattr_t
pthread_spinlock_t
pthread_t
timer_t
trace_attr_t
trace_event_id_t
trace_event_set_t
trace_id_t
```

Additionally:

- \*

  **mode\_t** shall be an integer type.

- \*

  **dev\_t** shall be an integer type.

- \*

  **nlink\_t**, **uid\_t**, **gid\_t**, and **id\_t** shall be integer types.

- \*

  **blkcnt\_t** and **off\_t** shall be signed integer types.

- \*

  **fsblkcnt\_t**, **fsfilcnt\_t**, and **ino\_t** shall be defined as unsigned integer types.

- \*

  **size\_t** shall be an unsigned integer type.

- \*

  **blksize\_t**, **pid\_t**, and **ssize\_t** shall be signed integer types.

- \*

  **clock\_t** shall be an integer or real-floating type. **time\_t** shall be an integer type.

The type **ssize\_t** shall be capable of storing values at least in the range \[-1, {SSIZE\_MAX}\].

The type **suseconds\_t** shall be a signed integer type capable of storing values at least in the range \[-1, 1000000\].

The implementation shall support one or more programming environments in which the widths of **blksize\_t**, **pid\_t**, **size\_t**, **ssize\_t**, and **suseconds\_t** are no greater than the width of type **long**. The names of these programming environments can be obtained using the *confstr*() function or the *getconf* utility.

There are no defined comparison or assignment operators for the following types:

```
pthread_attr_t
pthread_barrier_t
pthread_barrierattr_t
pthread_cond_t
pthread_condattr_t
pthread_mutex_t
pthread_mutexattr_t
pthread_rwlock_t
pthread_rwlockattr_t
pthread_spinlock_t
timer_t
trace_attr_t
```

*The following sections are informative.*

## APPLICATION USAGE

None.

## RATIONALE

None.

## FUTURE DIRECTIONS

None.

## SEE ALSO

***\<time.h\>***

The System Interfaces volume of POSIX.1‐2017, *confstr()*

The Shell and Utilities volume of POSIX.1‐2017, *getconf*

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting\_bugs.html .