22：参数错误，比如ip地址不合法，没有目标端口等
101：网络不可达，比如不能ping通
111：链接被拒绝，比如目标关闭链接等
115：当链接设置为非阻塞时，目标没有及时应答，返回此错误，socket可以继续使用
附录：Linux的错误码表（errno table)
_ 124 EMEDIUMTYPE_ Wrong medium type
_ 123 ENOMEDIUM__ No medium found
_ 122 EDQUOT___ Disk quota exceeded
_ 121 EREMOTEIO__ Remote I/O error
_ 120 EISNAM___ Is a named type file
_ 119 ENAVAIL___ No XENIX semaphores available
_ 118 ENOTNAM___ Not a XENIX named type file
_ 117 EUCLEAN___ Structure needs cleaning
_ 116 ESTALE___ Stale NFS file handle
_ 115 EINPROGRESS +Operation now in progress
_ 114 EALREADY__ Operation already in progress
_ 113 EHOSTUNREACH No route to host
_ 112 EHOSTDOWN__ Host is down
_ 111 ECONNREFUSED Connection refused
_ 110 ETIMEDOUT_ +Connection timed out
_ 109 ETOOMANYREFS Too many references: cannot splice
_ 108 ESHUTDOWN__ Cannot send after transport endpoint shutdown
_ 107 ENOTCONN__ Transport endpoint is not connected
_ 106 EISCONN___ Transport endpoint is already connected
_ 105 ENOBUFS___ No buffer space available
_ 104 ECONNRESET_ Connection reset by peer
_ 103 ECONNABORTED Software caused connection abort
_ 102 ENETRESET__ Network dropped connection on reset
_ 101 ENETUNREACH_ Network is unreachable
_ 100 ENETDOWN__ Network is down
_ 99 EADDRNOTAVAIL Cannot assign requested address
_ 98 EADDRINUSE_ Address already in use
_ 97 EAFNOSUPPORT Address family not supported by protocol
_ 96 EPFNOSUPPORT Protocol family not supported
_ 95 EOPNOTSUPP_ Operation not supported
_ 94 ESOCKTNOSUPPORT Socket type not supported
_ 93 EPROTONOSUPPORT Protocol not supported
_ 92 ENOPROTOOPT_ Protocol not available
_ 91 EPROTOTYPE_ Protocol wrong type for socket
_ 90 EMSGSIZE__ +Message too long
_ 89 EDESTADDRREQ Destination address required
_ 88 ENOTSOCK__ Socket operation on non-socket
_ 87 EUSERS___ Too many users
_ 86 ESTRPIPE__ Streams pipe error
_ 85 ERESTART__ Interrupted system call should be restarted
_ 84 EILSEQ___ Invalid or incomplete multibyte or wide character
_ 83 ELIBEXEC__ Cannot exec a shared library directly
_ 82 ELIBMAX___ Attempting to link in too many shared libraries
_ 81 ELIBSCN___ .lib section in a.out corrupted
_ 80 ELIBBAD___ Accessing a corrupted shared library
_ 79 ELIBACC___ Can not access a needed shared library
_ 78 EREMCHG___ Remote address changed
_ 77 EBADFD___ File descriptor in bad state
_ 76 ENOTUNIQ__ Name not unique on network
_ 75 EOVERFLOW__ Value too large for defined data type
_ 74 EBADMSG__ +Bad message
_ 73 EDOTDOT___ RFS specific error
_ 72 EMULTIHOP__ Multihop attempted
_ 71 EPROTO___ Protocol error
_ 70 ECOMM____ Communication error on send
_ 69 ESRMNT___ Srmount error
_ 68 EADV____ Advertise error
_ 67 ENOLINK___ Link has been severed
_ 66 EREMOTE___ Object is remote
_ 65 ENOPKG___ Package not installed
_ 64 ENONET___ Machine is not on the network
_ 63 ENOSR____ Out of streams resources
_ 62 ETIME____ Timer expired
_ 61 ENODATA___ No data available
_ 60 ENOSTR___ Device not a stream
_ 59 EBFONT___ Bad font file format
_ 57 EBADSLT___ Invalid slot
_ 56 EBADRQC___ Invalid request code
_ 55 ENOANO___ No anode
_ 54 EXFULL___ Exchange full
_ 53 EBADR____ Invalid request descriptor
_ 52 EBADE____ Invalid exchange
_ 51 EL2HLT___ Level 2 halted
_ 50 ENOCSI___ No CSI structure available
_ 49 EUNATCH___ Protocol driver not attached
_ 48 ELNRNG___ Link number out of range
_ 47 EL3RST___ Level 3 reset
_ 46 EL3HLT___ Level 3 halted
_ 45 EL2NSYNC__ Level 2 not synchronized
_ 44 ECHRNG___ Channel number out of range
_ 43 EIDRM____ Identifier removed
_ 42 ENOMSG___ No message of desired type
_ 40 ELOOP____ Too many levels of symbolic links
_ 39 ENOTEMPTY_ +Directory not empty
_ 38 ENOSYS___ +Function not implemented
_ 37 ENOLCK___ +No locks available
_ 36 ENAMETOOLONG +File name too long
_ 35 EDEADLK__ +Resource deadlock avoided
_ 34 ERANGE___ +Numerical result out of range
_ 33 EDOM____ +Numerical argument out of domain
_ 32 EPIPE___ +Broken pipe
_ 31 EMLINK___ +Too many links
_ 30 EROFS___ +Read-only file system
_ 29 ESPIPE___ +Illegal seek
_ 28 ENOSPC___ +No space left on device
_ 27 EFBIG___ +File too large
_ 26 ETXTBSY___ Text file busy
_ 25 ENOTTY___ +Inappropriate ioctl for device
_ 24 EMFILE___ +Too many open files
_ 23 ENFILE___ +Too many open files in system
_ 22 EINVAL___ +Invalid argument
_ 21 EISDIR___ +Is a directory
_ 20 ENOTDIR__ +Not a directory
_ 19 ENODEV___ +No such device
_ 18 EXDEV___ +Invalid cross-device link
_ 17 EEXIST___ +File exists
_ 16 EBUSY___ +Device or resource busy
_ 15 ENOTBLK___ Block device required
_ 14 EFAULT___ +Bad address
_ 13 EACCES___ +Permission denied
_ 12 ENOMEM___ +Cannot allocate memory
_ 11 EAGAIN___ +Resource temporarily unavailable
_ 10 ECHILD___ +No child processes
__ 9 EBADF___ +Bad file descriptor
__ 8 ENOEXEC__ +Exec format error
__ 7 E2BIG___ +Argument list too long
__ 6 ENXIO___ +No such device or address
__ 5 EIO____ +Input/output error
__ 4 EINTR___ +Interrupted system call
__ 3 ESRCH___ +No such process
__ 2 ENOENT___ +No such file or directory
__ 1 EPERM___ +Operation not permitted
#_ 0 --_____ Success