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1 | .\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>, |
2 | .\" Copyright (C) 2008-2014, Michael Kerrisk <mtk.manpages@gmail.com>, | |
3 | .\" and Copyright (C) 2016, Heinrich Schuchardt <xypron.glpk@gmx.de> | |
2297bf0e | 4 | .\" |
00acdba1 | 5 | .\" %%%LICENSE_START(VERBATIM_ONE_PARA) |
77117f4f MK |
6 | .\" Permission is granted to distribute possibly modified copies |
7 | .\" of this page provided the header is included verbatim, | |
8 | .\" and in case of nontrivial modification author and date | |
9 | .\" of the modification is added to the header. | |
8ff7380d | 10 | .\" %%%LICENSE_END |
77117f4f MK |
11 | .\" |
12 | .\" Modified, 2003-12-02, Michael Kerrisk, <mtk.manpages@gmail.com> | |
13 | .\" Modified, 2003-09-23, Adam Langley | |
14 | .\" Modified, 2004-05-27, Michael Kerrisk, <mtk.manpages@gmail.com> | |
15 | .\" Added SOCK_SEQPACKET | |
16 | .\" 2008-05-27, mtk, Provide a clear description of the three types of | |
17 | .\" address that can appear in the sockaddr_un structure: pathname, | |
18 | .\" unnamed, and abstract. | |
19 | .\" | |
63121bd4 | 20 | .TH UNIX 7 2019-08-02 "Linux" "Linux Programmer's Manual" |
77117f4f | 21 | .SH NAME |
f68512e9 | 22 | unix \- sockets for local interprocess communication |
77117f4f MK |
23 | .SH SYNOPSIS |
24 | .B #include <sys/socket.h> | |
25 | .br | |
26 | .B #include <sys/un.h> | |
f90f031e | 27 | .PP |
d4c8c97c | 28 | .IB unix_socket " = socket(AF_UNIX, type, 0);" |
77117f4f | 29 | .br |
d4c8c97c | 30 | .IB error " = socketpair(AF_UNIX, type, 0, int *" sv ");" |
77117f4f MK |
31 | .SH DESCRIPTION |
32 | The | |
d4c8c97c | 33 | .B AF_UNIX |
77117f4f | 34 | (also known as |
d4c8c97c | 35 | .BR AF_LOCAL ) |
77117f4f MK |
36 | socket family is used to communicate between processes on the same machine |
37 | efficiently. | |
4891f52a | 38 | Traditionally, UNIX domain sockets can be either unnamed, |
9ee4a2b6 | 39 | or bound to a filesystem pathname (marked as being of type socket). |
77117f4f | 40 | Linux also supports an abstract namespace which is independent of the |
9ee4a2b6 | 41 | filesystem. |
5711c04f | 42 | .PP |
d02879f7 | 43 | Valid socket types in the UNIX domain are: |
77117f4f | 44 | .BR SOCK_STREAM , |
d02879f7 | 45 | for a stream-oriented socket; |
77117f4f MK |
46 | .BR SOCK_DGRAM , |
47 | for a datagram-oriented socket that preserves message boundaries | |
008f1ecc | 48 | (as on most UNIX implementations, UNIX domain datagram |
77117f4f MK |
49 | sockets are always reliable and don't reorder datagrams); |
50 | and (since Linux 2.6.4) | |
51 | .BR SOCK_SEQPACKET , | |
0d7e8d59 MK |
52 | for a sequenced-packet socket that is connection-oriented, |
53 | preserves message boundaries, | |
77117f4f | 54 | and delivers messages in the order that they were sent. |
5711c04f | 55 | .PP |
4891f52a | 56 | UNIX domain sockets support passing file descriptors or process credentials |
77117f4f | 57 | to other processes using ancillary data. |
c634028a | 58 | .SS Address format |
008f1ecc | 59 | A UNIX domain socket address is represented in the following structure: |
e646a1ba | 60 | .PP |
77117f4f | 61 | .in +4n |
e646a1ba | 62 | .EX |
63bc262c | 63 | .\" #define UNIX_PATH_MAX 108 |
5ffdc2fd | 64 | .\" |
77117f4f MK |
65 | struct sockaddr_un { |
66 | sa_family_t sun_family; /* AF_UNIX */ | |
b65f4c69 | 67 | char sun_path[108]; /* Pathname */ |
77117f4f | 68 | }; |
b8302363 | 69 | .EE |
77117f4f MK |
70 | .in |
71 | .PP | |
d02879f7 | 72 | The |
77117f4f | 73 | .I sun_family |
d02879f7 | 74 | field always contains |
77117f4f | 75 | .BR AF_UNIX . |
05bf3361 | 76 | On Linux, |
840aa3c7 MK |
77 | .I sun_path |
78 | is 108 bytes in size; see also NOTES, below. | |
5711c04f | 79 | .PP |
d02879f7 MK |
80 | Various systems calls (for example, |
81 | .BR bind (2), | |
82 | .BR connect (2), | |
83 | and | |
84 | .BR sendto (2)) | |
85 | take a | |
b8017cf5 | 86 | .I sockaddr_un |
d02879f7 MK |
87 | argument as input. |
88 | Some other system calls (for example, | |
89 | .BR getsockname (2), | |
90 | .BR getpeername (2), | |
91 | .BR recvfrom (2), | |
92 | and | |
93 | .BR accept (2)) | |
94 | return an argument of this type. | |
5711c04f | 95 | .PP |
d02879f7 MK |
96 | Three types of address are distinguished in the |
97 | .I sockaddr_un | |
98 | structure: | |
77117f4f MK |
99 | .IP * 3 |
100 | .IR pathname : | |
1c7b2458 MK |
101 | a UNIX domain socket can be bound to a null-terminated |
102 | filesystem pathname using | |
77117f4f | 103 | .BR bind (2). |
d02879f7 MK |
104 | When the address of a pathname socket is returned |
105 | (by one of the system calls noted above), | |
77117f4f | 106 | its length is |
5711c04f | 107 | .IP |
6cd06646 | 108 | offsetof(struct sockaddr_un, sun_path) + strlen(sun_path) + 1 |
5711c04f | 109 | .IP |
77117f4f MK |
110 | and |
111 | .I sun_path | |
112 | contains the null-terminated pathname. | |
d02879f7 MK |
113 | (On Linux, the above |
114 | .BR offsetof () | |
115 | expression equates to the same value as | |
116 | .IR sizeof(sa_family_t) , | |
117 | but some other implementations include other fields before | |
118 | .IR sun_path , | |
119 | so the | |
120 | .BR offsetof () | |
121 | expression more portably describes the size of the address structure.) | |
122 | .IP | |
123 | For further details of pathname sockets, see below. | |
77117f4f MK |
124 | .IP * |
125 | .IR unnamed : | |
126 | A stream socket that has not been bound to a pathname using | |
127 | .BR bind (2) | |
128 | has no name. | |
129 | Likewise, the two sockets created by | |
130 | .BR socketpair (2) | |
131 | are unnamed. | |
d02879f7 | 132 | When the address of an unnamed socket is returned, |
77117f4f MK |
133 | its length is |
134 | .IR "sizeof(sa_family_t)" , | |
135 | and | |
136 | .I sun_path | |
137 | should not be inspected. | |
138 | .\" There is quite some variation across implementations: FreeBSD | |
139 | .\" says the length is 16 bytes, HP-UX 11 says it's zero bytes. | |
140 | .IP * | |
141 | .IR abstract : | |
d02879f7 MK |
142 | an abstract socket address is distinguished (from a pathname socket) |
143 | by the fact that | |
77117f4f | 144 | .IR sun_path[0] |
d1a71985 | 145 | is a null byte (\(aq\e0\(aq). |
156a0e0d MK |
146 | The socket's address in this namespace is given by the additional |
147 | bytes in | |
148 | .IR sun_path | |
149 | that are covered by the specified length of the address structure. | |
77117f4f | 150 | (Null bytes in the name have no special significance.) |
9ee4a2b6 | 151 | The name has no connection with filesystem pathnames. |
d02879f7 | 152 | When the address of an abstract socket is returned, |
156a0e0d MK |
153 | the returned |
154 | .I addrlen | |
155 | is greater than | |
156 | .IR "sizeof(sa_family_t)" | |
157 | (i.e., greater than 2), and the name of the socket is contained in | |
158 | the first | |
159 | .IR "(addrlen \- sizeof(sa_family_t))" | |
160 | bytes of | |
161 | .IR sun_path . | |
d02879f7 MK |
162 | .SS Pathname sockets |
163 | When binding a socket to a pathname, a few rules should be observed | |
164 | for maximum portability and ease of coding: | |
165 | .IP * 3 | |
166 | The pathname in | |
167 | .I sun_path | |
168 | should be null-terminated. | |
169 | .IP * | |
170 | The length of the pathname, including the terminating null byte, | |
171 | should not exceed the size of | |
172 | .IR sun_path . | |
173 | .IP * | |
174 | The | |
175 | .I addrlen | |
176 | argument that describes the enclosing | |
177 | .I sockaddr_un | |
178 | structure should have a value of at least: | |
5711c04f | 179 | .IP |
d02879f7 MK |
180 | .nf |
181 | offsetof(struct sockaddr_un, sun_path)+strlen(addr.sun_path)+1 | |
182 | .fi | |
183 | .IP | |
b8017cf5 | 184 | or, more simply, |
d02879f7 MK |
185 | .I addrlen |
186 | can be specified as | |
187 | .IR "sizeof(struct sockaddr_un)" . | |
188 | .PP | |
189 | There is some variation in how implementations handle UNIX domain | |
190 | socket addresses that do not follow the above rules. | |
191 | For example, some (but not all) implementations | |
192 | .\" Linux does this, including for the case where the supplied path | |
193 | .\" is 108 bytes | |
194 | append a null terminator if none is present in the supplied | |
195 | .IR sun_path . | |
5711c04f | 196 | .PP |
d02879f7 MK |
197 | When coding portable applications, |
198 | keep in mind that some implementations | |
199 | .\" HP-UX | |
200 | have | |
201 | .I sun_path | |
202 | as short as 92 bytes. | |
203 | .\" Modern BSDs generally have 104, Tru64 and AIX have 104, | |
204 | .\" Solaris and Irix have 108 | |
5711c04f | 205 | .PP |
d02879f7 MK |
206 | Various system calls |
207 | .RB ( accept (2), | |
208 | .BR recvfrom (2), | |
209 | .BR getsockname (2), | |
210 | .BR getpeername (2)) | |
211 | return socket address structures. | |
212 | When applied to UNIX domain sockets, the value-result | |
213 | .I addrlen | |
214 | argument supplied to the call should be initialized as above. | |
215 | Upon return, the argument is set to indicate the | |
216 | .I actual | |
217 | size of the address structure. | |
218 | The caller should check the value returned in this argument: | |
219 | if the output value exceeds the input value, | |
220 | then there is no guarantee that a null terminator is present in | |
221 | .IR sun_path . | |
222 | (See BUGS.) | |
9f213833 MK |
223 | .\" |
224 | .SS Pathname socket ownership and permissions | |
225 | In the Linux implementation, | |
226 | pathname sockets honor the permissions of the directory they are in. | |
a23d8efa | 227 | Creation of a new socket fails if the process does not have write and |
9f213833 | 228 | search (execute) permission on the directory in which the socket is created. |
5711c04f | 229 | .PP |
9f213833 MK |
230 | On Linux, |
231 | connecting to a stream socket object requires write permission on that socket; | |
232 | sending a datagram to a datagram socket likewise | |
233 | requires write permission on that socket. | |
234 | POSIX does not make any statement about the effect of the permissions | |
7f98a239 | 235 | on a socket file, and on some systems (e.g., older BSDs), |
9f213833 MK |
236 | the socket permissions are ignored. |
237 | Portable programs should not rely on | |
238 | this feature for security. | |
5711c04f | 239 | .PP |
9f213833 MK |
240 | When creating a new socket, the owner and group of the socket file |
241 | are set according to the usual rules. | |
242 | The socket file has all permissions enabled, | |
243 | other than those that are turned off by the process | |
244 | .BR umask (2). | |
5711c04f | 245 | .PP |
9f213833 MK |
246 | The owner, group, and permissions of a pathname socket can be changed (using |
247 | .BR chown (2) | |
248 | and | |
249 | .BR chmod (2)). | |
250 | .\" However, fchown() and fchmod() do not seem to have an effect | |
251 | .\" | |
d1875c13 | 252 | .SS Abstract sockets |
44cca454 MK |
253 | Socket permissions have no meaning for abstract sockets: |
254 | the process | |
255 | .BR umask (2) | |
256 | has no effect when binding an abstract socket, | |
257 | and changing the ownership and permissions of the object (via | |
258 | .BR fchown (2) | |
259 | and | |
260 | .BR fchmod (2)) | |
261 | has no effect on the accessibility of the socket. | |
5711c04f | 262 | .PP |
d1875c13 MK |
263 | Abstract sockets automatically disappear when all open references |
264 | to the socket are closed. | |
5711c04f | 265 | .PP |
d1875c13 MK |
266 | The abstract socket namespace is a nonportable Linux extension. |
267 | .\" | |
c634028a | 268 | .SS Socket options |
464b254b | 269 | For historical reasons, these socket options are specified with a |
77117f4f MK |
270 | .B SOL_SOCKET |
271 | type even though they are | |
d4c8c97c | 272 | .B AF_UNIX |
77117f4f MK |
273 | specific. |
274 | They can be set with | |
275 | .BR setsockopt (2) | |
276 | and read with | |
277 | .BR getsockopt (2) | |
278 | by specifying | |
279 | .B SOL_SOCKET | |
280 | as the socket family. | |
281 | .TP | |
282 | .B SO_PASSCRED | |
928c3e7c | 283 | Enabling this socket option causes receipt of the credentials of |
421d34c6 MK |
284 | the sending process in an |
285 | .B SCM_CREDENTIALS ancillary | |
928c3e7c | 286 | message in each subsequently received message. |
421d34c6 MK |
287 | The returned credentials are those specified by the sender using |
288 | .BR SCM_CREDENTIALS , | |
289 | or a default that includes the sender's PID, real user ID, and real group ID, | |
290 | if the sender did not specify | |
291 | .B SCM_CREDENTIALS | |
292 | ancillary data. | |
c02ed554 MK |
293 | .IP |
294 | When this option is set and the socket is not yet connected, | |
77117f4f | 295 | a unique name in the abstract namespace will be generated automatically. |
744c8fa8 MK |
296 | .IP |
297 | The value given as an argument to | |
298 | .BR setsockopt (2) | |
299 | and returned as the result of | |
300 | .BR getsockopt (2) | |
301 | is an integer boolean flag. | |
366a9bff MK |
302 | .TP |
303 | .B SO_PASSSEC | |
ffad6a01 MK |
304 | Enables receiving of the SELinux security label of the peer socket |
305 | in an ancillary message of type | |
306 | .BR SCM_SECURITY | |
307 | (see below). | |
744c8fa8 MK |
308 | .IP |
309 | The value given as an argument to | |
310 | .BR setsockopt (2) | |
311 | and returned as the result of | |
312 | .BR getsockopt (2) | |
313 | is an integer boolean flag. | |
314 | .IP | |
315 | The | |
316 | .B SO_PASSSEC | |
317 | option is supported for UNIX domain datagram sockets | |
366a9bff MK |
318 | .\" commit 877ce7c1b3afd69a9b1caeb1b9964c992641f52a |
319 | since Linux 2.6.18; | |
320 | support for UNIX domain stream sockets was added | |
321 | .\" commit 37a9a8df8ce9de6ea73349c9ac8bdf6ba4ec4f70 | |
322 | in Linux 4.2. | |
ffab8460 MK |
323 | .TP |
324 | .BR SO_PEEK_OFF | |
325 | See | |
326 | .BR socket (7). | |
94950b9a MK |
327 | .TP |
328 | .B SO_PEERCRED | |
3d3cddde MK |
329 | This read-only socket option returns the |
330 | credentials of the peer process connected to this socket. | |
94950b9a MK |
331 | The returned credentials are those that were in effect at the time |
332 | of the call to | |
333 | .BR connect (2) | |
334 | or | |
335 | .BR socketpair (2). | |
3d3cddde MK |
336 | .IP |
337 | The argument to | |
338 | .BR getsockopt (2) | |
339 | is a pointer to a | |
94950b9a MK |
340 | .I ucred |
341 | structure; define the | |
342 | .B _GNU_SOURCE | |
343 | feature test macro to obtain the definition of that structure from | |
344 | .IR <sys/socket.h> . | |
3d3cddde MK |
345 | .IP |
346 | The use of this option is possible only for connected | |
347 | .B AF_UNIX | |
348 | stream sockets and for | |
349 | .B AF_UNIX | |
350 | stream and datagram socket pairs created using | |
351 | .BR socketpair (2). | |
366a9bff | 352 | .\" |
c634028a | 353 | .SS Autobind feature |
0cf2caa4 | 354 | If a |
0b80cf56 | 355 | .BR bind (2) |
0cf2caa4 MK |
356 | call specifies |
357 | .I addrlen | |
358 | as | |
359 | .IR sizeof(sa_family_t) , | |
449dd4e2 | 360 | .\" i.e., sizeof(short) |
0cf2caa4 MK |
361 | or the |
362 | .BR SO_PASSCRED | |
363 | socket option was specified for a socket that was | |
364 | not explicitly bound to an address, | |
365 | then the socket is autobound to an abstract address. | |
366 | The address consists of a null byte | |
367 | followed by 5 bytes in the character set | |
9bc87ed0 | 368 | .IR [0\-9a\-f] . |
1e4e3bad MK |
369 | Thus, there is a limit of 2^20 autobind addresses. |
370 | (From Linux 2.1.15, when the autobind feature was added, | |
371 | 8 bytes were used, and the limit was thus 2^32 autobind addresses. | |
372 | The change to 5 bytes came in Linux 2.3.15.) | |
19e19f5f | 373 | .SS Sockets API |
77117f4f | 374 | The following paragraphs describe domain-specific details and |
008f1ecc | 375 | unsupported features of the sockets API for UNIX domain sockets on Linux. |
5711c04f | 376 | .PP |
008f1ecc | 377 | UNIX domain sockets do not support the transmission of |
77117f4f MK |
378 | out-of-band data (the |
379 | .B MSG_OOB | |
380 | flag for | |
381 | .BR send (2) | |
382 | and | |
383 | .BR recv (2)). | |
5711c04f | 384 | .PP |
77117f4f MK |
385 | The |
386 | .BR send (2) | |
387 | .B MSG_MORE | |
008f1ecc | 388 | flag is not supported by UNIX domain sockets. |
5711c04f | 389 | .PP |
c9a39fea MK |
390 | Before Linux 3.4, |
391 | .\" commit 9f6f9af7694ede6314bed281eec74d588ba9474f | |
392 | the use of | |
77e75b90 MK |
393 | .B MSG_TRUNC |
394 | in the | |
395 | .I flags | |
396 | argument of | |
397 | .BR recv (2) | |
c9a39fea | 398 | was not supported by UNIX domain sockets. |
5711c04f | 399 | .PP |
77117f4f MK |
400 | The |
401 | .B SO_SNDBUF | |
008f1ecc | 402 | socket option does have an effect for UNIX domain sockets, but the |
77117f4f MK |
403 | .B SO_RCVBUF |
404 | option does not. | |
405 | For datagram sockets, the | |
406 | .B SO_SNDBUF | |
407 | value imposes an upper limit on the size of outgoing datagrams. | |
408 | This limit is calculated as the doubled (see | |
409 | .BR socket (7)) | |
410 | option value less 32 bytes used for overhead. | |
c634028a | 411 | .SS Ancillary messages |
77117f4f MK |
412 | Ancillary data is sent and received using |
413 | .BR sendmsg (2) | |
414 | and | |
415 | .BR recvmsg (2). | |
05bf3361 | 416 | For historical reasons, the ancillary message types listed below |
77117f4f MK |
417 | are specified with a |
418 | .B SOL_SOCKET | |
419 | type even though they are | |
d4c8c97c | 420 | .B AF_UNIX |
77117f4f | 421 | specific. |
05bf3361 | 422 | To send them, set the |
77117f4f MK |
423 | .I cmsg_level |
424 | field of the struct | |
425 | .I cmsghdr | |
426 | to | |
427 | .B SOL_SOCKET | |
428 | and the | |
429 | .I cmsg_type | |
430 | field to the type. | |
05bf3361 | 431 | For more information, see |
77117f4f MK |
432 | .BR cmsg (3). |
433 | .TP | |
434 | .B SCM_RIGHTS | |
435 | Send or receive a set of open file descriptors from another process. | |
436 | The data portion contains an integer array of the file descriptors. | |
87996200 | 437 | .IP |
13600496 MK |
438 | Commonly, this operation is referred to as "passing a file descriptor" |
439 | to another process. | |
440 | However, more accurately, | |
441 | what is being passed is a reference to an open file description (see | |
442 | .BR open (2)), | |
443 | and in the receiving process it is likely that a different | |
444 | file descriptor number will be used. | |
445 | Semantically, this operation is equivalent to duplicating | |
446 | .RB ( dup (2)) | |
447 | a file descriptor into the file descriptor table of another process. | |
8bdcf4bf | 448 | .IP |
4564dd1f MK |
449 | If the buffer used to receive the ancillary data containing |
450 | file descriptors is too small (or is absent), | |
451 | then the ancillary data is truncated (or discarded) | |
452 | and the excess file descriptors are automatically closed | |
453 | in the receiving process. | |
454 | .IP | |
e2340cf7 MK |
455 | If the number of file descriptors received in the ancillary data would |
456 | cause the process to exceed its | |
457 | .B RLIMIT_NOFILE | |
458 | resource limit (see | |
459 | .BR getrlimit (2)), | |
460 | the excess file descriptors are automatically closed | |
461 | in the receiving process. | |
462 | .IP | |
8bdcf4bf MK |
463 | The kernel constant |
464 | .BR SCM_MAX_FD | |
465 | defines a limit on the number of file descriptors in the array. | |
1221abb6 | 466 | Attempting to send an array larger than this limit causes |
8bdcf4bf MK |
467 | .BR sendmsg (2) |
468 | to fail with the error | |
469 | .BR EINVAL . | |
470 | .BR SCM_MAX_FD | |
471 | has the value 253 | |
472 | (or 255 in kernels | |
473 | .\" commit bba14de98753cb6599a2dae0e520714b2153522d | |
474 | before 2.6.38). | |
77117f4f MK |
475 | .TP |
476 | .B SCM_CREDENTIALS | |
008f1ecc | 477 | Send or receive UNIX credentials. |
77117f4f MK |
478 | This can be used for authentication. |
479 | The credentials are passed as a | |
480 | .I struct ucred | |
481 | ancillary message. | |
b1587ca8 MK |
482 | Thus structure is defined in |
483 | .I <sys/socket.h> | |
484 | as follows: | |
5711c04f | 485 | .IP |
77117f4f | 486 | .in +4n |
b8302363 | 487 | .EX |
77117f4f | 488 | struct ucred { |
b65f4c69 MK |
489 | pid_t pid; /* Process ID of the sending process */ |
490 | uid_t uid; /* User ID of the sending process */ | |
491 | gid_t gid; /* Group ID of the sending process */ | |
77117f4f | 492 | }; |
b8302363 | 493 | .EE |
77117f4f | 494 | .in |
5711c04f | 495 | .IP |
b1587ca8 | 496 | Since glibc 2.8, the |
1bc510f5 | 497 | .B _GNU_SOURCE |
e417acb0 MK |
498 | feature test macro must be defined (before including |
499 | .I any | |
500 | header files) in order to obtain the definition | |
b1587ca8 | 501 | of this structure. |
5711c04f | 502 | .IP |
77117f4f | 503 | The credentials which the sender specifies are checked by the kernel. |
f1081bdc | 504 | A privileged process is allowed to specify values that do not match its own. |
77117f4f MK |
505 | The sender must specify its own process ID (unless it has the capability |
506 | .BR CAP_SYS_ADMIN ), | |
06b8a13b | 507 | its real user ID, effective user ID, or saved set-user-ID (unless it has |
77117f4f | 508 | .BR CAP_SETUID ), |
06b8a13b | 509 | and its real group ID, effective group ID, or saved set-group-ID |
77117f4f MK |
510 | (unless it has |
511 | .BR CAP_SETGID ). | |
bdef8021 | 512 | .IP |
77117f4f MK |
513 | To receive a |
514 | .I struct ucred | |
b66d5714 | 515 | message, the |
77117f4f MK |
516 | .B SO_PASSCRED |
517 | option must be enabled on the socket. | |
ffad6a01 MK |
518 | .TP |
519 | .B SCM_SECURITY | |
520 | Receive the SELinux security context (the security label) | |
521 | of the peer socket. | |
522 | The received ancillary data is a null-terminated string containing | |
523 | the security context. | |
524 | The receiver should allocate at least | |
525 | .BR NAME_MAX | |
526 | bytes in the data portion of the ancillary message for this data. | |
527 | .IP | |
528 | To receive the security context, the | |
529 | .B SO_PASSSEC | |
530 | option must be enabled on the socket (see above). | |
c8772146 | 531 | .PP |
5b5cb195 MK |
532 | When sending ancillary data with |
533 | .BR sendmsg (2), | |
534 | only one item of each of the above types may be included in the sent message. | |
535 | .PP | |
5219daec MK |
536 | At least one byte of real data should be sent when sending ancillary data. |
537 | On Linux, this is required to successfully send ancillary data over | |
538 | a UNIX domain stream socket. | |
539 | When sending ancillary data over a UNIX domain datagram socket, | |
540 | it is not necessary on Linux to send any accompanying real data. | |
541 | However, portable applications should also include at least one byte | |
542 | of real data when sending ancillary data over a datagram socket. | |
543 | .PP | |
5af0f223 MK |
544 | When receiving from a stream socket, |
545 | ancillary data forms a kind of barrier for the received data. | |
546 | For example, suppose that the sender transmits as follows: | |
547 | .PP | |
548 | .RS | |
549 | .PD 0 | |
550 | .IP 1. 3 | |
551 | .BR sendmsg (2) | |
552 | of four bytes, with no ancillary data. | |
553 | .IP 2. | |
554 | .BR sendmsg (2) | |
555 | of one byte, with ancillary data. | |
556 | .IP 3. | |
557 | .BR sendmsg (2) | |
558 | of four bytes, with no ancillary data. | |
559 | .PD | |
560 | .RE | |
561 | .PP | |
562 | Suppose that the receiver now performs | |
563 | .BR recvmsg (2) | |
564 | calls each with a buffer size of 20 bytes. | |
565 | The first call will receive five bytes of data, | |
566 | along with the ancillary data sent by the second | |
567 | .BR sendmsg (2) | |
568 | call. | |
569 | The next call will receive the remaining five bytes of data. | |
570 | .PP | |
c0e56ed6 | 571 | If the space allocated for receiving incoming ancillary data is too small |
c8772146 MK |
572 | then the ancillary data is truncated to the number of headers |
573 | that will fit in the supplied buffer (or, in the case of an | |
574 | .BR SCM_RIGHTS | |
575 | file descriptor list, the list of file descriptors may be truncated). | |
c0e56ed6 MK |
576 | If no buffer is provided for incoming ancillary data (i.e., the |
577 | .I msg_control | |
578 | field of the | |
579 | .I msghdr | |
580 | structure supplied to | |
581 | .BR recvmsg (2) | |
582 | is NULL), | |
583 | then the incoming ancillary data is discarded. | |
584 | In both of these cases, the | |
c8772146 MK |
585 | .BR MSG_CTRUNC |
586 | flag will be set in the | |
587 | .I msg.msg_flags | |
588 | value returned by | |
589 | .BR recvmsg (2). | |
590 | .\" | |
fbea0f81 MK |
591 | .SS Ioctls |
592 | The following | |
593 | .BR ioctl (2) | |
594 | calls return information in | |
595 | .IR value . | |
596 | The correct syntax is: | |
597 | .PP | |
598 | .RS | |
599 | .nf | |
600 | .BI int " value"; | |
f0d77d97 | 601 | .IB error " = ioctl(" unix_socket ", " ioctl_type ", &" value ");" |
fbea0f81 MK |
602 | .fi |
603 | .RE | |
604 | .PP | |
605 | .I ioctl_type | |
606 | can be: | |
607 | .TP | |
608 | .B SIOCINQ | |
170e5f0d JC |
609 | For |
610 | .B SOCK_STREAM | |
311bf2f6 | 611 | sockets, this call returns the number of unread bytes in the receive buffer. |
fbea0f81 MK |
612 | The socket must not be in LISTEN state, otherwise an error |
613 | .RB ( EINVAL ) | |
614 | is returned. | |
615 | .B SIOCINQ | |
616 | is defined in | |
617 | .IR <linux/sockios.h> . | |
bea08fec | 618 | .\" FIXME . http://sources.redhat.com/bugzilla/show_bug.cgi?id=12002, |
fbea0f81 MK |
619 | .\" filed 2010-09-10, may cause SIOCINQ to be defined in glibc headers |
620 | Alternatively, | |
621 | you can use the synonymous | |
622 | .BR FIONREAD , | |
623 | defined in | |
624 | .IR <sys/ioctl.h> . | |
7aed61d9 | 625 | .\" SIOCOUTQ also has an effect for UNIX domain sockets, but not |
fbea0f81 MK |
626 | .\" quite what userland might expect. It seems to return the number |
627 | .\" of bytes allocated for buffers containing pending output. | |
628 | .\" That number is normally larger than the number of bytes of pending | |
629 | .\" output. Since this info is, from userland's point of view, imprecise, | |
630 | .\" and it may well change, probably best not to document this now. | |
170e5f0d JC |
631 | For |
632 | .B SOCK_DGRAM | |
311bf2f6 | 633 | sockets, |
170e5f0d | 634 | the returned value is the same as |
311bf2f6 | 635 | for Internet domain datagram sockets; |
170e5f0d JC |
636 | see |
637 | .BR udp (7). | |
77117f4f MK |
638 | .SH ERRORS |
639 | .TP | |
640 | .B EADDRINUSE | |
9ee4a2b6 | 641 | The specified local address is already in use or the filesystem socket |
77117f4f MK |
642 | object already exists. |
643 | .TP | |
7934bcdf MK |
644 | .B EBADF |
645 | This error can occur for | |
646 | .BR sendmsg (2) | |
647 | when sending a file descriptor as ancillary data over | |
648 | a UNIX domain socket (see the description of | |
649 | .BR SCM_RIGHTS , | |
650 | above), and indicates that the file descriptor number that | |
3eb078c5 | 651 | is being sent is not valid (e.g., it is not an open file descriptor). |
7934bcdf | 652 | .TP |
77117f4f | 653 | .B ECONNREFUSED |
1fe284ab | 654 | The remote address specified by |
77117f4f | 655 | .BR connect (2) |
1fe284ab | 656 | was not a listening socket. |
d02879f7 | 657 | This error can also occur if the target pathname is not a socket. |
77117f4f MK |
658 | .TP |
659 | .B ECONNRESET | |
660 | Remote socket was unexpectedly closed. | |
661 | .TP | |
662 | .B EFAULT | |
663 | User memory address was not valid. | |
664 | .TP | |
665 | .B EINVAL | |
666 | Invalid argument passed. | |
1fe284ab | 667 | A common cause is that the value |
40656bc7 | 668 | .B AF_UNIX |
1fe284ab | 669 | was not specified in the |
77117f4f | 670 | .I sun_type |
1fe284ab | 671 | field of passed addresses, or the socket was in an |
77117f4f MK |
672 | invalid state for the applied operation. |
673 | .TP | |
674 | .B EISCONN | |
675 | .BR connect (2) | |
676 | called on an already connected socket or a target address was | |
677 | specified on a connected socket. | |
678 | .TP | |
ec55a2b6 MK |
679 | .B ENOENT |
680 | The pathname in the remote address specified to | |
9470f355 | 681 | .BR connect (2) |
ec55a2b6 MK |
682 | did not exist. |
683 | .TP | |
77117f4f MK |
684 | .B ENOMEM |
685 | Out of memory. | |
686 | .TP | |
687 | .B ENOTCONN | |
688 | Socket operation needs a target address, but the socket is not connected. | |
689 | .TP | |
690 | .B EOPNOTSUPP | |
691 | Stream operation called on non-stream oriented socket or tried to | |
692 | use the out-of-band data option. | |
693 | .TP | |
694 | .B EPERM | |
695 | The sender passed invalid credentials in the | |
696 | .IR "struct ucred" . | |
697 | .TP | |
698 | .B EPIPE | |
699 | Remote socket was closed on a stream socket. | |
700 | If enabled, a | |
701 | .B SIGPIPE | |
702 | is sent as well. | |
703 | This can be avoided by passing the | |
704 | .B MSG_NOSIGNAL | |
705 | flag to | |
110039c1 | 706 | .BR send (2) |
77117f4f | 707 | or |
110039c1 | 708 | .BR sendmsg (2). |
77117f4f MK |
709 | .TP |
710 | .B EPROTONOSUPPORT | |
cd0221ea MK |
711 | Passed protocol is not |
712 | .BR AF_UNIX . | |
77117f4f MK |
713 | .TP |
714 | .B EPROTOTYPE | |
715 | Remote socket does not match the local socket type | |
716 | .RB ( SOCK_DGRAM | |
d1c9ea80 | 717 | versus |
9ca2e0c1 | 718 | .BR SOCK_STREAM ). |
77117f4f MK |
719 | .TP |
720 | .B ESOCKTNOSUPPORT | |
721 | Unknown socket type. | |
dc4eea68 MK |
722 | .TP |
723 | .B ETOOMANYREFS | |
724 | This error can occur for | |
725 | .BR sendmsg (2) | |
4529d4e5 | 726 | when sending a file descriptor as ancillary data over |
dc4eea68 MK |
727 | a UNIX domain socket (see the description of |
728 | .BR SCM_RIGHTS , | |
729 | above). | |
730 | It occurs if the number of "in-flight" file descriptors exceeds the | |
731 | .B RLIMIT_NOFILE | |
732 | resource limit and the caller does not have the | |
733 | .BR CAP_SYS_RESOURCE | |
734 | capability. | |
735 | An in-flight file descriptor is one that has been sent using | |
736 | .BR sendmsg (2) | |
737 | but has not yet been accepted in the recipient process using | |
738 | .BR recvmsg (2). | |
5711c04f | 739 | .IP |
70fdcbc2 MK |
740 | This error is diagnosed since mainline Linux 4.5 |
741 | (and in some earlier kernel versions where the fix has been backported). | |
dc4eea68 MK |
742 | .\" commit 712f4aad406bb1ed67f3f98d04c044191f0ff593 |
743 | In earlier kernel versions, | |
744 | it was possible to place an unlimited number of file descriptors in flight, | |
745 | by sending each file descriptor with | |
746 | .BR sendmsg (2) | |
747 | and then closing the file descriptor so that it was not accounted against the | |
748 | .B RLIMIT_NOFILE | |
749 | resource limit. | |
77117f4f MK |
750 | .PP |
751 | Other errors can be generated by the generic socket layer or | |
9ee4a2b6 | 752 | by the filesystem while generating a filesystem socket object. |
77117f4f MK |
753 | See the appropriate manual pages for more information. |
754 | .SH VERSIONS | |
755 | .B SCM_CREDENTIALS | |
756 | and the abstract namespace were introduced with Linux 2.2 and should not | |
757 | be used in portable programs. | |
758 | (Some BSD-derived systems also support credential passing, | |
759 | but the implementation details differ.) | |
760 | .SH NOTES | |
00b78c5f MK |
761 | Binding to a socket with a filename creates a socket |
762 | in the filesystem that must be deleted by the caller when it is no | |
763 | longer needed (using | |
764 | .BR unlink (2)). | |
765 | The usual UNIX close-behind semantics apply; the socket can be unlinked | |
766 | at any time and will be finally removed from the filesystem when the last | |
767 | reference to it is closed. | |
5711c04f | 768 | .PP |
00b78c5f | 769 | To pass file descriptors or credentials over a |
d3e7786d MK |
770 | .BR SOCK_STREAM |
771 | socket, you must | |
00b78c5f MK |
772 | to send or receive at least one byte of nonancillary data in the same |
773 | .BR sendmsg (2) | |
774 | or | |
775 | .BR recvmsg (2) | |
776 | call. | |
5711c04f | 777 | .PP |
00b78c5f MK |
778 | UNIX domain stream sockets do not support the notion of out-of-band data. |
779 | .\" | |
d02879f7 MK |
780 | .SH BUGS |
781 | When binding a socket to an address, | |
782 | Linux is one of the implementations that appends a null terminator | |
783 | if none is supplied in | |
784 | .IR sun_path . | |
785 | In most cases this is unproblematic: | |
786 | when the socket address is retrieved, | |
787 | it will be one byte longer than that supplied when the socket was bound. | |
788 | However, there is one case where confusing behavior can result: | |
789 | if 108 non-null bytes are supplied when a socket is bound, | |
790 | then the addition of the null terminator takes the length of | |
791 | the pathname beyond | |
792 | .IR sizeof(sun_path) . | |
793 | Consequently, when retrieving the socket address | |
794 | (for example, via | |
795 | .BR accept (2)), | |
796 | .\" The behavior on Solaris is quite similar. | |
797 | if the input | |
798 | .I addrlen | |
799 | argument for the retrieving call is specified as | |
800 | .IR "sizeof(struct sockaddr_un)" , | |
801 | then the returned address structure | |
802 | .I won't | |
803 | have a null terminator in | |
804 | .IR sun_path . | |
5711c04f | 805 | .PP |
d02879f7 MK |
806 | In addition, some implementations |
807 | .\" i.e., traditional BSD | |
808 | don't require a null terminator when binding a socket (the | |
809 | .I addrlen | |
810 | argument is used to determine the length of | |
811 | .IR sun_path ) | |
812 | and when the socket address is retrieved on these implementations, | |
813 | there is no null terminator in | |
814 | .IR sun_path . | |
5711c04f | 815 | .PP |
b8017cf5 | 816 | Applications that retrieve socket addresses can (portably) code |
d02879f7 MK |
817 | to handle the possibility that there is no null terminator in |
818 | .IR sun_path | |
819 | by respecting the fact that the number of valid bytes in the pathname is: | |
5711c04f | 820 | .PP |
d02879f7 MK |
821 | strnlen(addr.sun_path, addrlen \- offsetof(sockaddr_un, sun_path)) |
822 | .\" The following patch to amend kernel behavior was rejected: | |
823 | .\" http://thread.gmane.org/gmane.linux.kernel.api/2437 | |
824 | .\" Subject: [patch] Fix handling of overlength pathname in AF_UNIX sun_path | |
825 | .\" 2012-04-17 | |
826 | .\" And there was a related discussion in the Austin list: | |
827 | .\" http://thread.gmane.org/gmane.comp.standards.posix.austin.general/5735 | |
828 | .\" Subject: Having a sun_path with no null terminator | |
829 | .\" 2012-04-18 | |
830 | .\" | |
831 | .\" FIXME . Track http://austingroupbugs.net/view.php?id=561 | |
5711c04f | 832 | .PP |
d02879f7 MK |
833 | Alternatively, an application can retrieve |
834 | the socket address by allocating a buffer of size | |
835 | .I "sizeof(struct sockaddr_un)+1" | |
836 | that is zeroed out before the retrieval. | |
837 | The retrieving call can specify | |
838 | .I addrlen | |
839 | as | |
840 | .IR "sizeof(struct sockaddr_un)" , | |
841 | and the extra zero byte ensures that there will be | |
842 | a null terminator for the string returned in | |
843 | .IR sun_path : | |
5711c04f | 844 | .PP |
a2b7a144 MK |
845 | .in +4n |
846 | .EX | |
d02879f7 MK |
847 | void *addrp; |
848 | ||
849 | addrlen = sizeof(struct sockaddr_un); | |
850 | addrp = malloc(addrlen + 1); | |
851 | if (addrp == NULL) | |
852 | /* Handle error */ ; | |
853 | memset(addrp, 0, addrlen + 1); | |
854 | ||
3e35b19b | 855 | if (getsockname(sfd, (struct sockaddr *) addrp, &addrlen)) == \-1) |
d02879f7 MK |
856 | /* handle error */ ; |
857 | ||
d1a71985 | 858 | printf("sun_path = %s\en", ((struct sockaddr_un *) addrp)\->sun_path); |
b8302363 | 859 | .EE |
e646a1ba | 860 | .in |
5711c04f | 861 | .PP |
d02879f7 MK |
862 | This sort of messiness can be avoided if it is guaranteed |
863 | that the applications that | |
864 | .I create | |
865 | pathname sockets follow the rules outlined above under | |
866 | .IR "Pathname sockets" . | |
77117f4f | 867 | .SH EXAMPLE |
84c8cae2 MK |
868 | The following code demonstrates the use of sequenced-packet |
869 | sockets for local interprocess communication. | |
eb73e8ad | 870 | It consists of two programs. |
15545eb6 | 871 | The server program waits for a connection from the client program. |
84c8cae2 MK |
872 | The client sends each of its command-line arguments in separate messages. |
873 | The server treats the incoming messages as integers and adds them up. | |
eb73e8ad | 874 | The client sends the command string "END". |
84c8cae2 MK |
875 | The server sends back a message containing the sum of the client's integers. |
876 | The client prints the sum and exits. | |
15545eb6 | 877 | The server waits for the next client to connect. |
84c8cae2 | 878 | To stop the server, the client is called with the command-line argument "DOWN". |
15545eb6 HS |
879 | .PP |
880 | The following output was recorded while running the server in the background | |
84c8cae2 MK |
881 | and repeatedly executing the client. |
882 | Execution of the server program ends when it receives the "DOWN" command. | |
15545eb6 HS |
883 | .SS Example output |
884 | .in +4n | |
b8302363 | 885 | .EX |
eb73e8ad | 886 | $ \fB./server &\fP |
15545eb6 | 887 | [1] 25887 |
eb73e8ad | 888 | $ \fB./client 3 4\fP |
15545eb6 | 889 | Result = 7 |
eb73e8ad | 890 | $ \fB./client 11 \-5\fP |
15545eb6 | 891 | Result = 6 |
eb73e8ad | 892 | $ \fB./client DOWN\fP |
15545eb6 HS |
893 | Result = 0 |
894 | [1]+ Done ./server | |
895 | $ | |
b8302363 | 896 | .EE |
15545eb6 HS |
897 | .in |
898 | .SS Program source | |
c7885256 | 899 | \& |
e7d0bb47 | 900 | .EX |
15545eb6 HS |
901 | /* |
902 | * File connection.h | |
903 | */ | |
904 | ||
905 | #define SOCKET_NAME "/tmp/9Lq7BNBnBycd6nxy.socket" | |
906 | #define BUFFER_SIZE 12 | |
907 | ||
908 | /* | |
909 | * File server.c | |
910 | */ | |
911 | ||
912 | #include <stdio.h> | |
913 | #include <stdlib.h> | |
914 | #include <string.h> | |
915 | #include <sys/socket.h> | |
916 | #include <sys/un.h> | |
917 | #include <unistd.h> | |
918 | #include "connection.h" | |
919 | ||
920 | int | |
921 | main(int argc, char *argv[]) | |
922 | { | |
923 | struct sockaddr_un name; | |
924 | int down_flag = 0; | |
925 | int ret; | |
926 | int connection_socket; | |
927 | int data_socket; | |
928 | int result; | |
929 | char buffer[BUFFER_SIZE]; | |
930 | ||
931 | /* | |
eb73e8ad | 932 | * In case the program exited inadvertently on the last run, |
15545eb6 HS |
933 | * remove the socket. |
934 | */ | |
935 | ||
936 | unlink(SOCKET_NAME); | |
937 | ||
938 | /* Create local socket. */ | |
939 | ||
940 | connection_socket = socket(AF_UNIX, SOCK_SEQPACKET, 0); | |
941 | if (connection_socket == \-1) { | |
942 | perror("socket"); | |
943 | exit(EXIT_FAILURE); | |
944 | } | |
945 | ||
946 | /* | |
eb73e8ad MK |
947 | * For portability clear the whole structure, since some |
948 | * implementations have additional (nonstandard) fields in | |
949 | * the structure. | |
15545eb6 HS |
950 | */ |
951 | ||
952 | memset(&name, 0, sizeof(struct sockaddr_un)); | |
953 | ||
954 | /* Bind socket to socket name. */ | |
955 | ||
956 | name.sun_family = AF_UNIX; | |
957 | strncpy(name.sun_path, SOCKET_NAME, sizeof(name.sun_path) \- 1); | |
958 | ||
959 | ret = bind(connection_socket, (const struct sockaddr *) &name, | |
960 | sizeof(struct sockaddr_un)); | |
961 | if (ret == \-1) { | |
962 | perror("bind"); | |
963 | exit(EXIT_FAILURE); | |
964 | } | |
965 | ||
966 | /* | |
eb73e8ad MK |
967 | * Prepare for accepting connections. The backlog size is set |
968 | * to 20. So while one request is being processed other requests | |
969 | * can be waiting. | |
15545eb6 HS |
970 | */ |
971 | ||
972 | ret = listen(connection_socket, 20); | |
973 | if (ret == \-1) { | |
974 | perror("listen"); | |
975 | exit(EXIT_FAILURE); | |
976 | } | |
977 | ||
978 | /* This is the main loop for handling connections. */ | |
979 | ||
980 | for (;;) { | |
981 | ||
15545eb6 HS |
982 | /* Wait for incoming connection. */ |
983 | ||
984 | data_socket = accept(connection_socket, NULL, NULL); | |
3cb43b95 | 985 | if (data_socket == \-1) { |
15545eb6 HS |
986 | perror("accept"); |
987 | exit(EXIT_FAILURE); | |
988 | } | |
989 | ||
990 | result = 0; | |
52900faa | 991 | for (;;) { |
15545eb6 HS |
992 | |
993 | /* Wait for next data packet. */ | |
994 | ||
995 | ret = read(data_socket, buffer, BUFFER_SIZE); | |
996 | if (ret == \-1) { | |
eb73e8ad | 997 | perror("read"); |
15545eb6 HS |
998 | exit(EXIT_FAILURE); |
999 | } | |
1000 | ||
1001 | /* Ensure buffer is 0\-terminated. */ | |
1002 | ||
1003 | buffer[BUFFER_SIZE \- 1] = 0; | |
1004 | ||
1005 | /* Handle commands. */ | |
1006 | ||
1007 | if (!strncmp(buffer, "DOWN", BUFFER_SIZE)) { | |
1008 | down_flag = 1; | |
1009 | break; | |
1010 | } | |
1011 | ||
1012 | if (!strncmp(buffer, "END", BUFFER_SIZE)) { | |
1013 | break; | |
1014 | } | |
1015 | ||
1016 | /* Add received summand. */ | |
1017 | ||
1018 | result += atoi(buffer); | |
1019 | } | |
c751683c | 1020 | |
15545eb6 HS |
1021 | /* Send result. */ |
1022 | ||
1023 | sprintf(buffer, "%d", result); | |
1024 | ret = write(data_socket, buffer, BUFFER_SIZE); | |
15545eb6 | 1025 | if (ret == \-1) { |
eb73e8ad | 1026 | perror("write"); |
15545eb6 HS |
1027 | exit(EXIT_FAILURE); |
1028 | } | |
1029 | ||
1030 | /* Close socket. */ | |
1031 | ||
1032 | close(data_socket); | |
1033 | ||
1034 | /* Quit on DOWN command. */ | |
1035 | ||
1036 | if (down_flag) { | |
1037 | break; | |
1038 | } | |
1039 | } | |
1040 | ||
1041 | close(connection_socket); | |
1042 | ||
1043 | /* Unlink the socket. */ | |
1044 | ||
1045 | unlink(SOCKET_NAME); | |
1046 | ||
1047 | exit(EXIT_SUCCESS); | |
1048 | } | |
1049 | ||
1050 | /* | |
1051 | * File client.c | |
1052 | */ | |
1053 | ||
1054 | #include <errno.h> | |
1055 | #include <stdio.h> | |
1056 | #include <stdlib.h> | |
1057 | #include <string.h> | |
1058 | #include <sys/socket.h> | |
1059 | #include <sys/un.h> | |
1060 | #include <unistd.h> | |
1061 | #include "connection.h" | |
1062 | ||
1063 | int | |
1064 | main(int argc, char *argv[]) | |
1065 | { | |
24a31d63 | 1066 | struct sockaddr_un addr; |
15545eb6 HS |
1067 | int i; |
1068 | int ret; | |
1069 | int data_socket; | |
1070 | char buffer[BUFFER_SIZE]; | |
1071 | ||
1072 | /* Create local socket. */ | |
1073 | ||
1074 | data_socket = socket(AF_UNIX, SOCK_SEQPACKET, 0); | |
1075 | if (data_socket == \-1) { | |
1076 | perror("socket"); | |
1077 | exit(EXIT_FAILURE); | |
1078 | } | |
1079 | ||
1080 | /* | |
eb73e8ad MK |
1081 | * For portability clear the whole structure, since some |
1082 | * implementations have additional (nonstandard) fields in | |
1083 | * the structure. | |
15545eb6 HS |
1084 | */ |
1085 | ||
24a31d63 | 1086 | memset(&addr, 0, sizeof(struct sockaddr_un)); |
15545eb6 | 1087 | |
24a31d63 | 1088 | /* Connect socket to socket address */ |
15545eb6 | 1089 | |
24a31d63 MK |
1090 | addr.sun_family = AF_UNIX; |
1091 | strncpy(addr.sun_path, SOCKET_NAME, sizeof(addr.sun_path) \- 1); | |
15545eb6 | 1092 | |
24a31d63 | 1093 | ret = connect (data_socket, (const struct sockaddr *) &addr, |
15545eb6 HS |
1094 | sizeof(struct sockaddr_un)); |
1095 | if (ret == \-1) { | |
d1a71985 | 1096 | fprintf(stderr, "The server is down.\en"); |
15545eb6 HS |
1097 | exit(EXIT_FAILURE); |
1098 | } | |
1099 | ||
1100 | /* Send arguments. */ | |
1101 | ||
1102 | for (i = 1; i < argc; ++i) { | |
1103 | ret = write(data_socket, argv[i], strlen(argv[i]) + 1); | |
1104 | if (ret == \-1) { | |
eb73e8ad | 1105 | perror("write"); |
15545eb6 HS |
1106 | break; |
1107 | } | |
1108 | } | |
1109 | ||
1110 | /* Request result. */ | |
1111 | ||
1112 | strcpy (buffer, "END"); | |
1113 | ret = write(data_socket, buffer, strlen(buffer) + 1); | |
1114 | if (ret == \-1) { | |
eb73e8ad | 1115 | perror("write"); |
15545eb6 HS |
1116 | exit(EXIT_FAILURE); |
1117 | } | |
1118 | ||
15545eb6 HS |
1119 | /* Receive result. */ |
1120 | ||
1121 | ret = read(data_socket, buffer, BUFFER_SIZE); | |
1122 | if (ret == \-1) { | |
eb73e8ad | 1123 | perror("read"); |
15545eb6 HS |
1124 | exit(EXIT_FAILURE); |
1125 | } | |
1126 | ||
1127 | /* Ensure buffer is 0\-terminated. */ | |
1128 | ||
1129 | buffer[BUFFER_SIZE \- 1] = 0; | |
1130 | ||
d1a71985 | 1131 | printf("Result = %s\en", buffer); |
15545eb6 HS |
1132 | |
1133 | /* Close socket. */ | |
1134 | ||
1135 | close(data_socket); | |
1136 | ||
1137 | exit(EXIT_SUCCESS); | |
1138 | } | |
e7d0bb47 | 1139 | .EE |
15545eb6 | 1140 | .PP |
c751683c MK |
1141 | For an example of the use of |
1142 | .BR SCM_RIGHTS | |
1143 | see | |
1144 | .BR cmsg (3). | |
47297adb | 1145 | .SH SEE ALSO |
77117f4f MK |
1146 | .BR recvmsg (2), |
1147 | .BR sendmsg (2), | |
1148 | .BR socket (2), | |
1149 | .BR socketpair (2), | |
1150 | .BR cmsg (3), | |
1151 | .BR capabilities (7), | |
1152 | .BR credentials (7), | |
170e5f0d JC |
1153 | .BR socket (7), |
1154 | .BR udp (7) |