Ubuntu下errno值

每当一个Unix函数(如socket函数）中发生错误时，全局变量errno将被设置成一个指示错误类型的正整数，如果函数不返回错误，errno的值就没有定义，值为0不表示任何错误.且具有以E开头的全大写字母名字，并且通常在/usr/include/sys/errno.h中定义，在Ubuntu中存放在/usr/include/asm-generic/errno.h,

为了方便查找，我们先给出errno.h在Ubuntu里面的内容

#ifndef _ASM_GENERIC_ERRNO_H
#define _ASM_GENERIC_ERRNO_H

#include <asm-generic/errno-base.h>

#define	EDEADLK		35	/* Resource deadlock would occur */
#define	ENAMETOOLONG	36	/* File name too long */
#define	ENOLCK		37	/* No record locks available */
#define	ENOSYS		38	/* Function not implemented */
#define	ENOTEMPTY	39	/* Directory not empty */
#define	ELOOP		40	/* Too many symbolic links encountered */
#define	EWOULDBLOCK	EAGAIN	/* Operation would block */
#define	ENOMSG		42	/* No message of desired type */
#define	EIDRM		43	/* Identifier removed */
#define	ECHRNG		44	/* Channel number out of range */
#define	EL2NSYNC	45	/* Level 2 not synchronized */
#define	EL3HLT		46	/* Level 3 halted */
#define	EL3RST		47	/* Level 3 reset */
#define	ELNRNG		48	/* Link number out of range */
#define	EUNATCH		49	/* Protocol driver not attached */
#define	ENOCSI		50	/* No CSI structure available */
#define	EL2HLT		51	/* Level 2 halted */
#define	EBADE		52	/* Invalid exchange */
#define	EBADR		53	/* Invalid request descriptor */
#define	EXFULL		54	/* Exchange full */
#define	ENOANO		55	/* No anode */
#define	EBADRQC		56	/* Invalid request code */
#define	EBADSLT		57	/* Invalid slot */

#define	EDEADLOCK	EDEADLK

#define	EBFONT		59	/* Bad font file format */
#define	ENOSTR		60	/* Device not a stream */
#define	ENODATA		61	/* No data available */
#define	ETIME		62	/* Timer expired */
#define	ENOSR		63	/* Out of streams resources */
#define	ENONET		64	/* Machine is not on the network */
#define	ENOPKG		65	/* Package not installed */
#define	EREMOTE		66	/* Object is remote */
#define	ENOLINK		67	/* Link has been severed */
#define	EADV		68	/* Advertise error */
#define	ESRMNT		69	/* Srmount error */
#define	ECOMM		70	/* Communication error on send */
#define	EPROTO		71	/* Protocol error */
#define	EMULTIHOP	72	/* Multihop attempted */
#define	EDOTDOT		73	/* RFS specific error */
#define	EBADMSG		74	/* Not a data message */
#define	EOVERFLOW	75	/* Value too large for defined data type */
#define	ENOTUNIQ	76	/* Name not unique on network */
#define	EBADFD		77	/* File descriptor in bad state */
#define	EREMCHG		78	/* Remote address changed */
#define	ELIBACC		79	/* Can not access a needed shared library */
#define	ELIBBAD		80	/* Accessing a corrupted shared library */
#define	ELIBSCN		81	/* .lib section in a.out corrupted */
#define	ELIBMAX		82	/* Attempting to link in too many shared libraries */
#define	ELIBEXEC	83	/* Cannot exec a shared library directly */
#define	EILSEQ		84	/* Illegal byte sequence */
#define	ERESTART	85	/* Interrupted system call should be restarted */
#define	ESTRPIPE	86	/* Streams pipe error */
#define	EUSERS		87	/* Too many users */
#define	ENOTSOCK	88	/* Socket operation on non-socket */
#define	EDESTADDRREQ	89	/* Destination address required */
#define	EMSGSIZE	90	/* Message too long */
#define	EPROTOTYPE	91	/* Protocol wrong type for socket */
#define	ENOPROTOOPT	92	/* Protocol not available */
#define	EPROTONOSUPPORT	93	/* Protocol not supported */
#define	ESOCKTNOSUPPORT	94	/* Socket type not supported */
#define	EOPNOTSUPP	95	/* Operation not supported on transport endpoint */
#define	EPFNOSUPPORT	96	/* Protocol family not supported */
#define	EAFNOSUPPORT	97	/* Address family not supported by protocol */
#define	EADDRINUSE	98	/* Address already in use */
#define	EADDRNOTAVAIL	99	/* Cannot assign requested address */
#define	ENETDOWN	100	/* Network is down */
#define	ENETUNREACH	101	/* Network is unreachable */
#define	ENETRESET	102	/* Network dropped connection because of reset */
#define	ECONNABORTED	103	/* Software caused connection abort */
#define	ECONNRESET	104	/* Connection reset by peer */
#define	ENOBUFS		105	/* No buffer space available */
#define	EISCONN		106	/* Transport endpoint is already connected */
#define	ENOTCONN	107	/* Transport endpoint is not connected */
#define	ESHUTDOWN	108	/* Cannot send after transport endpoint shutdown */
#define	ETOOMANYREFS	109	/* Too many references: cannot splice */
#define	ETIMEDOUT	110	/* Connection timed out */
#define	ECONNREFUSED	111	/* Connection refused */
#define	EHOSTDOWN	112	/* Host is down */
#define	EHOSTUNREACH	113	/* No route to host */
#define	EALREADY	114	/* Operation already in progress */
#define	EINPROGRESS	115	/* Operation now in progress */
#define	ESTALE		116	/* Stale NFS file handle */
#define	EUCLEAN		117	/* Structure needs cleaning */
#define	ENOTNAM		118	/* Not a XENIX named type file */
#define	ENAVAIL		119	/* No XENIX semaphores available */
#define	EISNAM		120	/* Is a named type file */
#define	EREMOTEIO	121	/* Remote I/O error */
#define	EDQUOT		122	/* Quota exceeded */

#define	ENOMEDIUM	123	/* No medium found */
#define	EMEDIUMTYPE	124	/* Wrong medium type */
#define	ECANCELED	125	/* Operation Canceled */
#define	ENOKEY		126	/* Required key not available */
#define	EKEYEXPIRED	127	/* Key has expired */
#define	EKEYREVOKED	128	/* Key has been revoked */
#define	EKEYREJECTED	129	/* Key was rejected by service */

/* for robust mutexes */
#define	EOWNERDEAD	130	/* Owner died */
#define	ENOTRECOVERABLE	131	/* State not recoverable */

#define ERFKILL		132	/* Operation not possible due to RF-kill */

#endif

在实际操作中，怎么在系统中实时查询errno.h的值呢？举一个用TCP协议获取服务器时间的例子。注意socket函数的第一参数已经由AF_INET改为9999.

#include	"unp.h"

int main(int argc, char **argv)
{
	int					sockfd, n;
	char				recvline[MAXLINE + 1];
	struct sockaddr_in	servaddr;

	if (argc != 2)
		err_quit("usage: a.out <IPaddress>");

	if ( (sockfd = socket(9999, SOCK_STREAM, 0)) < 0)
		err_sys("socket error");

	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port   = htons(13);	/* daytime server */
	if (inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0)
		err_quit("inet_pton error for %s", argv[1]);

	if (connect(sockfd, (SA *) &servaddr, sizeof(servaddr)) < 0)
		err_sys("connect error");

	while ( (n = read(sockfd, recvline, MAXLINE)) > 0) {
		recvline[n] = 0;	/* null terminate */
		if (fputs(recvline, stdout) == EOF)
			err_sys("fputs error");
	}
	if (n < 0)
		err_sys("read error");

	exit(0);
}

运行

make daytimetcpcli
./daytimetcpcli 127.0.0.1

要找出有关这个错误的详细信息，我们首先在errno.h头文件中使用grep查找字符串Address family not supported by protocol

grep 'Address family not supported by protocol' /usr/include/asm-generic/errno.h

#define	EAFNOSUPPORT	97	/* Address family not supported by protocol */

这就是由socket返回的errno.h值,我们然后查看手册页面.

man socket

大多数手册在最下面的Errors标题给出额外的信息，不过一般都很简洁

意思就是不支持指定的地址家族，就是说AF_INET那个地方改成了9999，不支持这个地址家族。应该改成AF_INET或者AF_INET6等等.