uname man page


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.

uname — return system name


uname [-amnrsv]


By default, the uname utility shall write the operating system name to standard output. When options are specified, symbols representing one or more system characteristics shall be written to the standard output. The format and contents of the symbols are implementation-defined. On systems conforming to the System Interfaces volume of POSIX.1‐2008, the symbols written shall be those supported by the uname() function as defined in the System Interfaces volume of POSIX.1‐2008.


The uname utility shall conform to the Base Definitions volume of POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.

The following options shall be supported:

Behave as though all of the options -mnrsv were specified.
Write the name of the hardware type on which the system is running to standard output.
Write the name of this node within an implementation-defined communications network.
Write the current release level of the operating system implementation.
Write the name of the implementation of the operating system.
Write the current version level of this release of the operating system implementation.

If no options are specified, the uname utility shall write the operating system name, as if the -s option had been specified.


Not used.

Environment Variables

The following environment variables shall affect the execution of uname:

Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1‐2008, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
If set to a non-empty string value, override the values of all the other internationalization variables.
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).
Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
Determine the location of message catalogs for the processing of LC_MESSAGES.

Asynchronous Events



By default, the output shall be a single line of the following form:

"%s\n", <sysname>

If the -a option is specified, the output shall be a single line of the following form:

"%s %s %s %s %s\n", <sysname>, <nodename>, <release>,
    <version>, <machine>

Additional implementation-defined symbols may be written; all such symbols shall be written at the end of the line of output before the <newline>.

If options are specified to select different combinations of the symbols, only those symbols shall be written, in the order shown above for the -a option. If a symbol is not selected for writing, its corresponding trailing <blank> characters also shall not be written.


The standard error shall be used only for diagnostic messages.

Exit Status

The following exit values shall be returned:

The requested information was successfully written.
An error occurred.

Consequences of Errors


The following sections are informative.

Application Usage

Note that any of the symbols could include embedded <space> characters, which may affect parsing algorithms if multiple options are selected for output.

The node name is typically a name that the system uses to identify itself for inter-system communication addressing.


The following command:

uname -sr

writes the operating system name and release level, separated by one or more <blank> characters.


It was suggested that this utility cannot be used portably since the format of the symbols is implementation-defined. The POSIX.1 working group could not achieve consensus on defining these formats in the underlying uname() function, and there was no expectation that this volume of POSIX.1‐2008 would be any more successful. Some applications may still find this historical utility of value. For example, the symbols could be used for system log entries or for comparison with operator or user input.

See Also

The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines

The System Interfaces volume of POSIX.1‐2008, uname()