1ERRNO(3) Linux Programmer's Manual ERRNO(3)
2
6 errno - number of last error
7
9 #include <errno.h>
10
12 The <errno.h> header file defines the integer variable errno, which is
13 set by system calls and some library functions in the event of an error
14 to indicate what went wrong. Its value is significant only when the
15 return value of the call indicated an error (i.e., -1 from most system
16 calls; -1 or NULL from most library functions); a function that suc‐
17 ceeds is allowed to change errno.
18 Valid error numbers are all nonzero; errno is never set to zero by any
20 system call or library function.
21 For some system calls and library functions (e.g., getpriority(2)), -1
23 is a valid return on success. In such cases, a successful return can
24 be distinguished from an error return by setting errno to zero before
25 the call, and then, if the call returns a status that indicates that an
26 error may have occurred, checking to see if errno has a nonzero value.
27 errno is defined by the ISO C standard to be a modifiable lvalue of
29 type int, and must not be explicitly declared; errno may be a macro.
30 errno is thread-local; setting it in one thread does not affect its
31 value in any other thread.
32 All the error names specified by POSIX.1 must have distinct values,
34 with the exception of EAGAIN and EWOULDBLOCK, which may be the same.
35 Below is a list of the symbolic error names that are defined on Linux.
37 Some of these are marked POSIX.1, indicating that the name is defined
38 by POSIX.1-2001, or C99, indicating that the name is defined by C99.
39 E2BIG Argument list too long (POSIX.1)
41 EACCES Permission denied (POSIX.1)
43 EADDRINUSE Address already in use (POSIX.1)
45 EADDRNOTAVAIL Address not available (POSIX.1)
47 EAFNOSUPPORT Address family not supported (POSIX.1)
49 EAGAIN Resource temporarily unavailable (may be the same value
51 as EWOULDBLOCK) (POSIX.1)
52 EALREADY Connection already in progress (POSIX.1)
54 EBADE Invalid exchange
56 EBADF Bad file descriptor (POSIX.1)
58 EBADFD File descriptor in bad state
60 EBADMSG Bad message (POSIX.1)
62 EBADR Invalid request descriptor
64 EBADRQC Invalid request code
66 EBADSLT Invalid slot
68 EBUSY Device or resource busy (POSIX.1)
70 ECANCELED Operation canceled (POSIX.1)
72 ECHILD No child processes (POSIX.1)
74 ECHRNG Channel number out of range
76 ECOMM Communication error on send
78 ECONNABORTED Connection aborted (POSIX.1)
80 ECONNREFUSED Connection refused (POSIX.1)
82 ECONNRESET Connection reset (POSIX.1)
84 EDEADLK Resource deadlock avoided (POSIX.1)
86 EDEADLOCK Synonym for EDEADLK
88 EDESTADDRREQ Destination address required (POSIX.1)
90 EDOM Mathematics argument out of domain of function
92 (POSIX.1, C99)
93 EDQUOT Disk quota exceeded (POSIX.1)
95 EEXIST File exists (POSIX.1)
97 EFAULT Bad address (POSIX.1)
99 EFBIG File too large (POSIX.1)
101 EHOSTDOWN Host is down
103 EHOSTUNREACH Host is unreachable (POSIX.1)
105 EIDRM Identifier removed (POSIX.1)
107 EILSEQ Illegal byte sequence (POSIX.1, C99)
109 EINPROGRESS Operation in progress (POSIX.1)
111 EINTR Interrupted function call (POSIX.1); see signal(7).
113 EINVAL Invalid argument (POSIX.1)
115 EIO Input/output error (POSIX.1)
117 EISCONN Socket is connected (POSIX.1)
119 EISDIR Is a directory (POSIX.1)
121 EISNAM Is a named type file
123 EKEYEXPIRED Key has expired
125 EKEYREJECTED Key was rejected by service
127 EKEYREVOKED Key has been revoked
129 EL2HLT Level 2 halted
131 EL2NSYNC Level 2 not synchronized
133 EL3HLT Level 3 halted
135 EL3RST Level 3 halted
137 ELIBACC Cannot access a needed shared library
139 ELIBBAD Accessing a corrupted shared library
141 ELIBMAX Attempting to link in too many shared libraries
143 ELIBSCN lib section in a.out corrupted
145 ELIBEXEC Cannot exec a shared library directly
147 ELOOP Too many levels of symbolic links (POSIX.1)
149 EMEDIUMTYPE Wrong medium type
151 EMFILE Too many open files (POSIX.1)
153 EMLINK Too many links (POSIX.1)
155 EMSGSIZE Message too long (POSIX.1)
157 EMULTIHOP Multihop attempted (POSIX.1)
159 ENAMETOOLONG Filename too long (POSIX.1)
161 ENETDOWN Network is down (POSIX.1)
163 ENETRESET Connection aborted by network (POSIX.1)
165 ENETUNREACH Network unreachable (POSIX.1)
167 ENFILE Too many open files in system (POSIX.1)
169 ENOBUFS No buffer space available (POSIX.1 (XSI STREAMS
171 option))
172 ENODATA No message is available on the STREAM head read queue
174 (POSIX.1)
175 ENODEV No such device (POSIX.1)
177 ENOENT No such file or directory (POSIX.1)
179 ENOEXEC Exec format error (POSIX.1)
181 ENOKEY Required key not available
183 ENOLCK No locks available (POSIX.1)
185 ENOLINK Link has been severed (POSIX.1)
187 ENOMEDIUM No medium found
189 ENOMEM Not enough space (POSIX.1)
191 ENOMSG No message of the desired type (POSIX.1)
193 ENONET Machine is not on the network
195 ENOPKG Package not installed
197 ENOPROTOOPT Protocol not available (POSIX.1)
199 ENOSPC No space left on device (POSIX.1)
201 ENOSR No STREAM resources (POSIX.1 (XSI STREAMS option))
203 ENOSTR Not a STREAM (POSIX.1 (XSI STREAMS option))
205 ENOSYS Function not implemented (POSIX.1)
207 ENOTBLK Block device required
209 ENOTCONN The socket is not connected (POSIX.1)
211 ENOTDIR Not a directory (POSIX.1)
213 ENOTEMPTY Directory not empty (POSIX.1)
215 ENOTSOCK Not a socket (POSIX.1)
217 ENOTSUP Operation not supported (POSIX.1)
219 ENOTTY Inappropriate I/O control operation (POSIX.1)
221 ENOTUNIQ Name not unique on network
223 ENXIO No such device or address (POSIX.1)
225 EOPNOTSUPP Operation not supported on socket (POSIX.1)
227 (ENOTSUP and EOPNOTSUPP have the same value on Linux,
229 but according to POSIX.1 these error values should be
230 distinct.)
231 EOVERFLOW Value too large to be stored in data type (POSIX.1)
233 EPERM Operation not permitted (POSIX.1)
235 EPFNOSUPPORT Protocol family not supported
237 EPIPE Broken pipe (POSIX.1)
239 EPROTO Protocol error (POSIX.1)
241 EPROTONOSUPPORT Protocol not supported (POSIX.1)
243 EPROTOTYPE Protocol wrong type for socket (POSIX.1)
245 ERANGE Result too large (POSIX.1, C99)
247 EREMCHG Remote address changed
249 EREMOTE Object is remote
251 EREMOTEIO Remote I/O error
253 ERESTART Interrupted system call should be restarted
255 EROFS Read-only file system (POSIX.1)
257 ESHUTDOWN Cannot send after transport endpoint shutdown
259 ESPIPE Invalid seek (POSIX.1)
261 ESOCKTNOSUPPORT Socket type not supported
263 ESRCH No such process (POSIX.1)
265 ESTALE Stale file handle (POSIX.1)
267 This error can occur for NFS and for other file systems
269 ESTRPIPE Streams pipe error
271 ETIME Timer expired (POSIX.1 (XSI STREAMS option))
273 (POSIX.1 says "STREAM ioctl(2) timeout")
275 ETIMEDOUT Connection timed out (POSIX.1)
277 ETXTBSY Text file busy (POSIX.1)
279 EUCLEAN Structure needs cleaning
281 EUNATCH Protocol driver not attached
283 EUSERS Too many users
285 EWOULDBLOCK Operation would block (may be same value as EAGAIN)
287 (POSIX.1)
288 EXDEV Improper link (POSIX.1)
290 EXFULL Exchange full
292
294 A common mistake is to do
295 if (somecall() == -1) {
297 printf("somecall() failed\n");
298 if (errno == ...) { ... }
299 }
300 where errno no longer needs to have the value it had upon return from
302 somecall() (i.e., it may have been changed by the printf(3)). If the
303 value of errno should be preserved across a library call, it must be
304 saved:
305 if (somecall() == -1) {
307 int errsv = errno;
308 printf("somecall() failed\n");
309 if (errsv == ...) { ... }
310 }
311 It was common in traditional C to declare errno manually (i.e., extern
313 int errno) instead of including <errno.h>. Do not do this. It will
314 not work with modern versions of the C library. However, on (very) old
315 UNIX systems, there may be no <errno.h> and the declaration is needed.
316
318 err(3), error(3), perror(3), strerror(3)
319
321 This page is part of release 3.53 of the Linux man-pages project. A
322 description of the project, and information about reporting bugs, can
323 be found at http://www.kernel.org/doc/man-pages/.
324 2008-07-09 ERRNO(3)