| PERROR(3) | Linux Programmer's Manual | PERROR(3) |
perror - print a system error message
#include <stdio.h>
void perror(const char *s);
#include <errno.h>
const char * const sys_errlist[];
int sys_nerr;
int errno; /* Not really declared this way; see errno(3)
*/
sys_errlist, sys_nerr:
From glibc 2.19 to 2.31:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_BSD_SOURCE
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.
Since glibc version 2.32, the declarations of sys_errlist and sys_nerr are no longer exposed by <stdio.h>.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
| perror () | Thread safety | MT-Safe race:stderr |
perror(), errno: POSIX.1-2001, POSIX.1-2008, C89, C99, 4.3BSD.
The externals sys_nerr and sys_errlist derive from BSD, but are not specified in POSIX.1.
The externals sys_nerr and sys_errlist are defined by glibc, but in <stdio.h>.
This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
| 2020-11-01 |