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.
logname — return the user's login name
The logname utility shall write the user's login name to standard output.
The login name shall be the string that would be returned by the
getlogin() function defined in the System Interfaces volume of
POSIX.1‐2017. Under the conditions where the getlogin() function
would fail, the logname utility shall write a diagnostic message to
standard error and exit with a non-zero exit status.
The following environment variables shall affect the execution of
The logname utility output shall be a single line consisting of the
user's login name:
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
- Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1‐2017,
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
- 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
- Successful completion.
- An error occurred.
The following sections are informative.
The logname utility explicitly ignores the LOGNAME environment
variable because environment changes could produce erroneous results.
The passwd file is not listed as required because the implementation may
have other means of mapping login names.
The Base Definitions volume of POSIX.1‐2017, Chapter
8, Environment Variables
The System Interfaces volume of POSIX.1‐2017,
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1-2017, Standard for Information Technology -- Portable Operating
System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018
Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html .
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