NAME

mkfifo — make FIFO special files

SYNOPSIS

mkfifo [-m mode] file...

DESCRIPTION

The mkfifo utility shall create the FIFO special files specified by the operands, in the order specified.

For each file operand, the mkfifo utility shall perform actions equivalent to the mkfifo() function defined in the System Interfaces volume of POSIX.1-2024, called with the following arguments:

1. The file operand is used as the path argument.

2. The value of the bitwise-inclusive OR of S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH is used as the mode argument. (If the -m option is specified, the value of the mkfifo() mode argument is unspecified, but the FIFO shall at no time have permissions less restrictive than the -m mode option-argument.)

OPTIONS

The mkfifo utility shall conform to XBD 12.2 Utility Syntax Guidelines.

The following option shall be supported:

-m mode

Set the file permission bits of the newly-created FIFO to the specified mode value. The mode option-argument shall be the same as the mode operand defined for the chmod utility. In the symbolic_mode strings, the op characters '+' and '-' shall be interpreted relative to an assumed initial mode of a=rw.

OPERANDS

The following operand shall be supported:

file

A pathname of the FIFO special file to be created.

STDIN

Not used.

INPUT FILES

None.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of mkfifo:

LANG

Provide a default value for the internationalization variables that are unset or null. (See XBD 8.2 Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)

LC_ALL

If set to a non-empty string value, override the values of all the other internationalization variables.

LC_CTYPE

Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments).

LC_MESSAGES

Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.

NLSPATH

^[XSI] Determine the location of messages objects and message catalogs.

ASYNCHRONOUS EVENTS

Default.

STDOUT

Not used.

STDERR

The standard error shall be used only for diagnostic messages.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

The following exit values shall be returned:

 0

All the specified FIFO special files were created successfully.

>0

An error occurred.

CONSEQUENCES OF ERRORS

Default.

APPLICATION USAGE

None.

EXAMPLES

None.

RATIONALE

This utility was added to permit shell applications to create FIFO special files.

The -m option was added to control the file mode, for consistency with the similar functionality provided by the mkdir utility.

Early proposals included a -p option similar to the mkdir -p option that created intermediate directories leading up to the FIFO specified by the final component. This was removed because it is not commonly needed and is not common practice with similar utilities.

The functionality of mkfifo is described substantially through a reference to the mkfifo() function in the System Interfaces volume of POSIX.1-2024. For example, by default, the mode of the FIFO file is affected by the file mode creation mask in accordance with the specified behavior of the mkfifo() function. In this way, there is less duplication of effort required for describing details of the file creation.

FUTURE DIRECTIONS

If this utility is directed to create a new directory entry that contains any bytes that have the encoded value of a <newline> character, implementations are encouraged to treat this as an error. A future version of this standard may require implementations to treat this as an error.

SEE ALSO

chmod, umask

XBD 8. Environment Variables, 12.2 Utility Syntax Guidelines

XSH mkfifo

CHANGE HISTORY

First released in Issue 3.

Issue 6

The -m option is aligned with the IEEE P1003.2b draft standard to clarify an ambiguity.

Issue 8

Austin Group Defect 251 is applied, encouraging implementations to disallow the creation of filenames containing any bytes that have the encoded value of a <newline> character.

Austin Group Defect 1122 is applied, changing the description of NLSPATH .