---
name: "explain_waitpid"
section: "3"
platform: "linux"
package: "libexplain-dev"
version: "1.4.D001-16"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/explain_waitpid"
---

# explain\_waitpid(3)

explain waitpid(2) errors

## NAME

explain\_waitpid - explain [waitpid(2)](/waitpid/2.md) errors

## SYNOPSIS

\#include \<libexplain/waitpid.h\>

const char \*explain\_waitpid(int pid, int \*status, int options);\
 const char \*explain\_errno\_waitpid(int errnum, int pid, int \*status, int options);\
 void explain\_message\_waitpid(char \*message, int message\_size, int pid, int \*status, int options);\
 void explain\_message\_errno\_waitpid(char \*message, int message\_size, int errnum, int pid, int \*status, int options);

## DESCRIPTION

These functions may be used to obtain explanations for errors returned by the [*waitpid*(2)](/waitpid/2.md) system call.

### explain\_waitpid

const char \*explain\_waitpid(int pid, int \*status, int options);

The **explain\_waitpid** function is used to obtain an explanation of an error returned by the [*waitpid*(2)](/waitpid/2.md) system call.  The least the message will contain is the value of `strerror(errno)`, but usually it will do much better, and indicate the underlying cause in more detail.

The *errno* global variable will be used to obtain the error value to be decoded.

This function is intended to be used in a fashion similar to the following example:

```
if (waitpid(pid, status, options) < 0)
{
    fprintf(stderr, "%s\n", explain_waitpid(pid, status, options));
    exit(EXIT_FAILURE);
}
```

- *pid*

  The original pid, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

- *status*

  The original status, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

- *options*

  The original options, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

- Returns:

  The message explaining the error.  This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list.  This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads.

**Note:** This function is **not** thread safe, because it shares a return buffer across all threads, and many other functions in this library.

### explain\_errno\_waitpid

const char \*explain\_errno\_waitpid(int errnum, int pid, int \*status, int options);

The **explain\_errno\_waitpid** function is used to obtain an explanation of an error returned by the [*waitpid*(2)](/waitpid/2.md) system call. The least the message will contain is the value of `strerror(errnum)`, but usually it will do much better, and indicate the underlying cause in more detail.

This function is intended to be used in a fashion similar to the following example:

```
if (waitpid(pid, status, options) < 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_waitpid(err,
        pid, status, options));
    exit(EXIT_FAILURE);
}
```

- *errnum*

  The error value to be decoded, usually obtained from the *errno* global variable just before this function is called.  This is necessary if you need to call **any** code between the system call to be explained and this function, because many libc functions will alter the value of *errno*.

- *pid*

  The original pid, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

- *status*

  The original status, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

- *options*

  The original options, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

- Returns:

  The message explaining the error.  This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list.  This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads.

**Note:** This function is **not** thread safe, because it shares a return buffer across all threads, and many other functions in this library.

### explain\_message\_waitpid

void explain\_message\_waitpid(char \*message, int message\_size, int pid, int \*status, int options);

The **explain\_message\_waitpid** function may be used to  obtain an explanation of an error returned by the [*waitpid*(2)](/waitpid/2.md) system call. The least the message will contain is the value of `strerror(errno)`, but usually it will do much better, and indicate the underlying cause in more detail.

The *errno* global variable will be used to obtain the error value to be decoded.

This function is intended to be used in a fashion similar to the following example:

```
if (waitpid(pid, status, options) < 0)
{
    char message[3000];
    explain_message_waitpid(message, sizeof(message), pid, status, options);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}
```

- *message*

  The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.

- *message\_size*

  The size in bytes of the location in which to store the returned message.

- *pid*

  The original pid, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

- *status*

  The original status, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

- *options*

  The original options, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

### explain\_message\_errno\_waitpid

void explain\_message\_errno\_waitpid(char \*message, int message\_size, int errnum, int pid, int \*status, int options);

The **explain\_message\_errno\_waitpid** function may be used to obtain an explanation of an error returned by the [*waitpid*(2)](/waitpid/2.md) system call. The least the message will contain is the value of `strerror(errnum)`, but usually it will do much better, and indicate the underlying cause in more detail.

This function is intended to be used in a fashion similar to the following example:

```
if (waitpid(pid, status, options) < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_waitpid(message, sizeof(message), err,
        pid, status, options);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}
```

- *message*

  The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.

- *message\_size*

  The size in bytes of the location in which to store the returned message.

- *errnum*

  The error value to be decoded, usually obtained from the *errno* global variable just before this function is called.  This is necessary if you need to call **any** code between the system call to be explained and this function, because many libc functions will alter the value of *errno*.

- *pid*

  The original pid, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

- *status*

  The original status, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

- *options*

  The original options, exactly as passed to the [*waitpid*(2)](/waitpid/2.md) system call.

## SEE ALSO

- [*waitpid*(2)](/waitpid/2.md)

  wait for process to change state

- [*explain\_waitpid\_or\_die*(3)](/explain_waitpid_or_die/3.md)

  wait for process to change state and report errors

## COPYRIGHT

libexplain version 1.4\
 Copyright (C) 2008 Peter Miller