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

# explain\_setpgrp(3)

explain setpgrp(2) errors

## NAME

explain\_setpgrp - explain [*setpgrp*(2)](/setpgrp/2.md) errors

## SYNOPSIS

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

const char \*explain\_setpgrp(pid\_t pid, pid\_t pgid);\
 const char \*explain\_errno\_setpgrp(int errnum, pid\_t pid, pid\_t pgid);\
 void explain\_message\_setpgrp(char \*message, int message\_size, pid\_t pid, pid\_t pgid);\
 void explain\_message\_errno\_setpgrp(char \*message, int message\_size, int errnum, pid\_t pid, pid\_t pgid);

## DESCRIPTION

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

**Note:** the [*setpgrp*(2)](/setpgrp/2.md) function has two implementations. The System V version has no arguments, while the BSD version has two arguments.  For simplicity of implementation, the argument list seen here includes the *pid* and *pgid* arguments.

The System V `getpgid()` semantics can be obtained by calling `setpgrp(0, 0)` on systems with the BSD version, and this is the API for libexplain, even on systems that do not use the BSD API.

### explain\_setpgrp

const char \*explain\_setpgrp(pid\_t pid, pid\_t pgid);

The **explain\_setpgrp** function is used to obtain an explanation of an error returned by the [*setpgrp*(2)](/setpgrp/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.

- *pid*

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

- *pgid*

  The original pgid, exactly as passed to the [*setpgrp*(2)](/setpgrp/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.

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

`if (setpgrp(pid, pgid) < 0)`

```
{
```

`fprintf(stderr, "%s\n", explain_setpgrp(pid, pgid));`

```
    exit(EXIT_FAILURE);
}
```

The above code example is available pre-packaged as the [*explain\_setpgrp\_or\_die*(3)](/explain_setpgrp_or_die/3.md) function.

### explain\_errno\_setpgrp

const char \*explain\_errno\_setpgrp(int errnum, pid\_t pid, pid\_t pgid);

The **explain\_errno\_setpgrp** function is used to obtain an explanation of an error returned by the [*setpgrp*(2)](/setpgrp/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.

- *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 [*setpgrp*(2)](/setpgrp/2.md) system call.

- *pgid*

  The original pgid, exactly as passed to the [*setpgrp*(2)](/setpgrp/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.

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

`if (setpgrp(pid, pgid) < 0)`

```
{
    int err = errno;
```

`fprintf(stderr, "%s\n", explain_errno_setpgrp(err, pid, pgid));`

```
    exit(EXIT_FAILURE);
}
```

The above code example is available pre-packaged as the [*explain\_setpgrp\_or\_die*(3)](/explain_setpgrp_or_die/3.md) function.

### explain\_message\_setpgrp

void explain\_message\_setpgrp(char \*message, int message\_size, pid\_t pid, pid\_t pgid);

The **explain\_message\_setpgrp** function is used to obtain an explanation of an error returned by the [*setpgrp*(2)](/setpgrp/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.

- *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 [*setpgrp*(2)](/setpgrp/2.md) system call.

- *pgid*

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

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

`if (setpgrp(pid, pgid) < 0)`

```
{
    char message[3000];
```

`explain_message_setpgrp(message, sizeof(message), pid, pgid);`

```
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}
```

The above code example is available pre-packaged as the [*explain\_setpgrp\_or\_die*(3)](/explain_setpgrp_or_die/3.md) function.

### explain\_message\_errno\_setpgrp

void explain\_message\_errno\_setpgrp(char \*message, int message\_size, int errnum, pid\_t pid, pid\_t pgid);

The **explain\_message\_errno\_setpgrp** function is used to obtain an explanation of an error returned by the [*setpgrp*(2)](/setpgrp/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.

- *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 [*setpgrp*(2)](/setpgrp/2.md) system call.

- *pgid*

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

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

`if (setpgrp(pid, pgid) < 0)`

```
{
    int err = errno;
    char message[3000];
```

`explain_message_errno_setpgrp(message, sizeof(message), err, pid, pgid);`

```
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}
```

The above code example is available pre-packaged as the [*explain\_setpgrp\_or\_die*(3)](/explain_setpgrp_or_die/3.md) function.

## SEE ALSO

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

  set process group

- [*explain\_setpgrp\_or\_die*(3)](/explain_setpgrp_or_die/3.md)

  set process group and report errors

## COPYRIGHT

libexplain version 1.4\
 Copyright (C) 2011 Peter Miller