---
name: "__syscall"
section: "2"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/__syscall"
---

# \_\_syscall(2)

indirect system call

## NAME

**syscall**, **\_\_syscall** – indirect system call

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<sys/syscall.h\>**

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

*int*\

**syscall**(*int number*, *...*);

*off\_t*\

**\_\_syscall**(*quad\_t number*, *...*);

## DESCRIPTION

The **syscall**() function performs the system call whose assembly language interface has the specified *number* with the specified arguments. Symbolic constants for system calls can be found in the header file ⟨sys/syscall.h⟩. The **\_\_syscall**() form should be used when one or more of the arguments is a 64-bit argument to ensure that argument alignment is correct. This system call is useful for testing new system calls that do not have entries in the C library.

## RETURN VALUES

The return values are defined by the system call being invoked. In general, a 0 return value indicates success. A -1 return value indicates an error, and an error code is stored in *errno*.

## HISTORY

The **syscall**() function appeared in 4.0BSD.

## BUGS

There is no way to simulate system calls that have multiple return values such as [pipe(2)](/pipe/2.md).