perror(3)                  Library Functions Manual                  perror(3)

NAME
       perror - print a system error message

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <stdio.h>

       void perror(const char *s);

       #include <errno.h>

       int errno;       /* Not really declared this way; see errno(3) */

       [[deprecated]] const char *const sys_errlist[];
       [[deprecated]] int sys_nerr;

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sys_errlist, sys_nerr:
           From glibc 2.19 to glibc 2.31:
               _DEFAULT_SOURCE
           glibc 2.19 and earlier:
               _BSD_SOURCE

DESCRIPTION
       The perror() function produces a message on standard error describing
       the last error encountered during a call to a system or library
       function.

       First (if s is not NULL and *s is not a null byte ('\0')), the argument
       string s is printed, followed by a colon and a blank.  Then an error
       message corresponding to the current value of errno and a new-line.

       To be of most use, the argument string should include the name of the
       function that incurred the error.

       The global error list sys_errlist[], which can be indexed by errno, can
       be used to obtain the error message without the newline.  The largest
       message number provided in the table is sys_nerr-1.  Be careful when
       directly accessing this list, because new error values may not have
       been added to sys_errlist[].  The use of sys_errlist[] is nowadays
       deprecated; use strerror(3) instead.

       When a system call fails, it usually returns -1 and sets the variable
       errno to a value describing what went wrong.  (These values can be
       found in <errno.h>.) Many library functions do likewise.  The function
       perror() serves to translate this error code into human-readable form.
       Note that errno is undefined after a successful system call or library
       function call: this call may well change this variable, even though it
       succeeds, for example because it internally used some other library
       function that failed.  Thus, if a failing call is not immediately
       followed by a call to perror(), the value of errno should be saved.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +--------------------------------+---------------+---------------------+
       |Interface                       | Attribute     | Value               |
       +--------------------------------+---------------+---------------------+
       |perror ()                       | Thread safety | MT-Safe race:stderr |
       +--------------------------------+---------------+---------------------+
STANDARDS
       errno
       perror()
              C11, POSIX.1-2008.

       sys_nerr
       sys_errlist
              BSD.

HISTORY
       errno
       perror()
              POSIX.1-2001, C89, 4.3BSD.

       sys_nerr
       sys_errlist
              Removed in glibc 2.32.

SEE ALSO
       err(3), errno(3), error(3), strerror(3)

Linux man-pages 6.7               2023-10-31                         perror(3)