1ERRNO(3)                   Linux Programmer's Manual                  ERRNO(3)
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NAME

6       errno - number of last error
7

SYNOPSIS

9       #include <errno.h>
10

DESCRIPTION

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
19       Valid error numbers are all non-zero; errno is never set to zero by any
20       system call or library function.
21
22       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 non-zero value.
27
28       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
33       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
36       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
40       E2BIG           Argument list too long (POSIX.1)
41
42       EACCES          Permission denied (POSIX.1)
43
44       EADDRINUSE      Address already in use (POSIX.1)
45
46       EADDRNOTAVAIL   Address not available (POSIX.1)
47
48       EAFNOSUPPORT    Address family not supported (POSIX.1)
49
50       EAGAIN          Resource temporarily unavailable (may be the same value
51                       as EWOULDBLOCK) (POSIX.1)
52
53       EALREADY        Connection already in progress (POSIX.1)
54
55       EBADE           Invalid exchange
56
57       EBADF           Bad file descriptor (POSIX.1)
58
59       EBADFD          File descriptor in bad state
60
61       EBADMSG         Bad message (POSIX.1)
62
63       EBADR           Invalid request descriptor
64
65       EBADRQC         Invalid request code
66
67       EBADSLT         Invalid slot
68
69       EBUSY           Device or resource busy (POSIX.1)
70
71       ECANCELED       Operation canceled (POSIX.1)
72
73       ECHILD          No child processes (POSIX.1)
74
75       ECHRNG          Channel number out of range
76
77       ECOMM           Communication error on send
78
79       ECONNABORTED    Connection aborted (POSIX.1)
80
81       ECONNREFUSED    Connection refused (POSIX.1)
82
83       ECONNRESET      Connection reset (POSIX.1)
84
85       EDEADLK         Resource deadlock avoided (POSIX.1)
86
87       EDEADLOCK       Synonym for EDEADLK
88
89       EDESTADDRREQ    Destination address required (POSIX.1)
90
91       EDOM            Mathematics  argument  out  of   domain   of   function
92                       (POSIX.1, C99)
93
94       EDQUOT          Disk quota exceeded (POSIX.1)
95
96       EEXIST          File exists (POSIX.1)
97
98       EFAULT          Bad address (POSIX.1)
99
100       EFBIG           File too large (POSIX.1)
101
102       EHOSTDOWN       Host is down
103
104       EHOSTUNREACH    Host is unreachable (POSIX.1)
105
106       EIDRM           Identifier removed (POSIX.1)
107
108       EILSEQ          Illegal byte sequence (POSIX.1, C99)
109
110       EINPROGRESS     Operation in progress (POSIX.1)
111
112       EINTR           Interrupted function call (POSIX.1); see signal(7).
113
114       EINVAL          Invalid argument (POSIX.1)
115
116       EIO             Input/output error (POSIX.1)
117
118       EISCONN         Socket is connected (POSIX.1)
119
120       EISDIR          Is a directory (POSIX.1)
121
122       EISNAM          Is a named type file
123
124       EKEYEXPIRED     Key has expired
125
126       EKEYREJECTED    Key was rejected by service
127
128       EKEYREVOKED     Key has been revoked
129
130       EL2HLT          Level 2 halted
131
132       EL2NSYNC        Level 2 not synchronized
133
134       EL3HLT          Level 3 halted
135
136       EL3RST          Level 3 halted
137
138       ELIBACC         Cannot access a needed shared library
139
140       ELIBBAD         Accessing a corrupted shared library
141
142       ELIBMAX         Attempting to link in too many shared libraries
143
144       ELIBSCN         lib section in a.out corrupted
145
146       ELIBEXEC        Cannot exec a shared library directly
147
148       ELOOP           Too many levels of symbolic links (POSIX.1)
149
150       EMEDIUMTYPE     Wrong medium type
151
152       EMFILE          Too many open files (POSIX.1)
153
154       EMLINK          Too many links (POSIX.1)
155
156       EMSGSIZE        Message too long (POSIX.1)
157
158       EMULTIHOP       Multihop attempted (POSIX.1)
159
160       ENAMETOOLONG    Filename too long (POSIX.1)
161
162       ENETDOWN        Network is down (POSIX.1)
163
164       ENETRESET       Connection aborted by network (POSIX.1)
165
166       ENETUNREACH     Network unreachable (POSIX.1)
167
168       ENFILE          Too many open files in system (POSIX.1)
169
170       ENOBUFS         No   buffer   space  available  (POSIX.1  (XSI  STREAMS
171                       option))
172
173       ENODATA         No message is available on the STREAM head  read  queue
174                       (POSIX.1)
175
176       ENODEV          No such device (POSIX.1)
177
178       ENOENT          No such file or directory (POSIX.1)
179
180       ENOEXEC         Exec format error (POSIX.1)
181
182       ENOKEY          Required key not available
183
184       ENOLCK          No locks available (POSIX.1)
185
186       ENOLINK         Link has been severed (POSIX.1)
187
188       ENOMEDIUM       No medium found
189
190       ENOMEM          Not enough space (POSIX.1)
191
192       ENOMSG          No message of the desired type (POSIX.1)
193
194       ENONET          Machine is not on the network
195
196       ENOPKG          Package not installed
197
198       ENOPROTOOPT     Protocol not available (POSIX.1)
199
200       ENOSPC          No space left on device (POSIX.1)
201
202       ENOSR           No STREAM resources (POSIX.1 (XSI STREAMS option))
203
204       ENOSTR          Not a STREAM (POSIX.1 (XSI STREAMS option))
205
206       ENOSYS          Function not implemented (POSIX.1)
207
208       ENOTBLK         Block device required
209
210       ENOTCONN        The socket is not connected (POSIX.1)
211
212       ENOTDIR         Not a directory (POSIX.1)
213
214       ENOTEMPTY       Directory not empty (POSIX.1)
215
216       ENOTSOCK        Not a socket (POSIX.1)
217
218       ENOTSUP         Operation not supported (POSIX.1)
219
220       ENOTTY          Inappropriate I/O control operation (POSIX.1)
221
222       ENOTUNIQ        Name not unique on network
223
224       ENXIO           No such device or address (POSIX.1)
225
226       EOPNOTSUPP      Operation not supported on socket (POSIX.1)
227
228                       (ENOTSUP  and  EOPNOTSUPP have the same value on Linux,
229                       but according to POSIX.1 these error values  should  be
230                       distinct.)
231
232       EOVERFLOW       Value too large to be stored in data type (POSIX.1)
233
234       EPERM           Operation not permitted (POSIX.1)
235
236       EPFNOSUPPORT    Protocol family not supported
237
238       EPIPE           Broken pipe (POSIX.1)
239
240       EPROTO          Protocol error (POSIX.1)
241
242       EPROTONOSUPPORT Protocol not supported (POSIX.1)
243
244       EPROTOTYPE      Protocol wrong type for socket (POSIX.1)
245
246       ERANGE          Result too large (POSIX.1, C99)
247
248       EREMCHG         Remote address changed
249
250       EREMOTE         Object is remote
251
252       EREMOTEIO       Remote I/O error
253
254       ERESTART        Interrupted system call should be restarted
255
256       EROFS           Read-only file system (POSIX.1)
257
258       ESHUTDOWN       Cannot send after transport endpoint shutdown
259
260       ESPIPE          Invalid seek (POSIX.1)
261
262       ESOCKTNOSUPPORT Socket type not supported
263
264       ESRCH           No such process (POSIX.1)
265
266       ESTALE          Stale file handle (POSIX.1)
267
268                       This error can occur for NFS and for other file systems
269
270       ESTRPIPE        Streams pipe error
271
272       ETIME           Timer expired (POSIX.1 (XSI STREAMS option))
273
274                       (POSIX.1 says "STREAM ioctl(2) timeout")
275
276       ETIMEDOUT       Connection timed out (POSIX.1)
277
278       ETXTBSY         Text file busy (POSIX.1)
279
280       EUCLEAN         Structure needs cleaning
281
282       EUNATCH         Protocol driver not attached
283
284       EUSERS          Too many users
285
286       EWOULDBLOCK     Operation  would  block  (may  be same value as EAGAIN)
287                       (POSIX.1)
288
289       EXDEV           Improper link (POSIX.1)
290
291       EXFULL          Exchange full
292

NOTES

294       A common mistake is to do
295
296           if (somecall() == -1) {
297               printf("somecall() failed\n");
298               if (errno == ...) { ... }
299           }
300
301       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
306           if (somecall() == -1) {
307               int errsv = errno;
308               printf("somecall() failed\n");
309               if (errsv == ...) { ... }
310           }
311
312       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

SEE ALSO

318       err(3), error(3), perror(3), strerror(3)
319

COLOPHON

321       This page is part of release 3.22 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/.
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327                                  2008-07-09                          ERRNO(3)
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