mysql localhost登录和tcp/ip登录

小结：
1 mysql的账户名格式为 user@host，host为%时表示匹配任意主机或ip，但是localhost除外，也就是说必须为localhost显示创建账号；
2 登录mysql时若指定localhost选项则采用unix socket，而非tcp/ip协议；

以下为验证过程，
1 localhost VS % 的登录权限
先创建一个用户，其host为%，当前数据库没有localhost匿名用户

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 mysql> grant select on *.* to 'test1'@'%' identified by 'test1';
 Query OK, 0 rows affected (0.00 sec)
 mysql> select host,user,password from mysql.user order by 1 desc ,2;
 +-----------------------------------------+--------------+-------------------------------------------+
 | host | user | password |
 +-----------------------------------------+--------------+-------------------------------------------+
 | localhost | root | |
 | ::1 | root | |
 | 127.0.0.1 | root | |
 | % | root | *96B86EC8D3F883B0C55D488A951E11B037E74816 |
 | % | test1 | *06C0BF5B64ECE2F648B5F048A71903906BA08E5C |
 +-----------------------------------------+--------------+-------------------------------------------+
 11 rows in set (0.00 sec)

尝试以unix socket方式登录，均失败

点击(此处)折叠或打开

 [root@mysqlslave3 ~]# /data1-new/app/services/mysql55d/bin/mysql --socket=/data1-new/app/tmp/mysql55d.sock -utest1 -ptest1
 ERROR 1045 (28000): Access denied for user 'test1'@'localhost' (using password: YES)
 [root@mysqlslave3 ~]# /data1-new/app/services/mysql55d/bin/mysql -utest1 -ptest1 --socket=/data1-new/app/tmp/mysql55d.sock -hlocalhost
 ERROR 1045 (28000): Access denied for user 'test1'@'localhost' (using password: YES)

另外，即便指定了socket选项，-h127.0.0.1也会强制采用tcp/ip连接登录

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 [root@mysqlslave3 ~]# /data1-new/app/services/mysql55d/bin/mysql --socket=/data1-new/app/tmp/mysql55d.sock -utest1 -ptest1 -h127.0.0.1
 mysql> status
 --------------
 /data1-new/app/services/mysql55d/bin/mysql Ver 14.14 Distrib 5.5.31, for Linux (x86_64) using readline 5.1
 Connection id:1449940
 Current database:
 Current user:test1@127.0.0.1
 SSL:Not in use
 Current pager:stdout
 Using outfile:''
 Using delimiter:;
 Server version:5.5.31-log Source distribution
 Protocol version:10
 Connection:127.0.0.1 via TCP/IP
 Server characterset:utf8
 Db characterset:utf8
 Client characterset:utf8
 Conn. characterset:utf8
 TCP port:3306
 Uptime:79 days 12 hours 22 min 29 sec

 Threads: 1 Questions: 4746519297 Slow queries: 144823 Opens: 18675 Flush tables: 79 Open tables: 24 Queries per second avg: 690.890

 mysql> select user(),current_user();
 +-----------------+----------------+
 | user() | current_user() |
 +-----------------+----------------+
 | test1@127.0.0.1 | test1@% |
 +-----------------+----------------+
 1 row in set (0.00 sec)

创建基于localhost的用户，

点击(此处)折叠或打开

 mysql> grant select on *.* to 'test1'@'localhost' identified by 'test1';
 Query OK, 0 rows affected (0.00 sec)
 mysql> select host,user,password from mysql.user order by 1 desc ,2;
 +-----------------------------------------+--------------+-------------------------------------------+
 | host | user | password |
 +-----------------------------------------+--------------+-------------------------------------------+
 | localhost | root | |
 | localhost | test1 | *06C0BF5B64ECE2F648B5F048A71903906BA08E5C |
 | ::1 | root | |
 | 127.0.0.1 | root | |
 | % | root | *96B86EC8D3F883B0C55D488A951E11B037E74816 |
 | % | test1 | *06C0BF5B64ECE2F648B5F048A71903906BA08E5C |
 +-----------------------------------------+--------------+-------------------------------------------+
 11 rows in set (0.00 sec)

再次以unix socket方式登录，成功

点击(此处)折叠或打开

 [root@mysqlslave3 ~]# /data1-new/app/services/mysql55d/bin/mysql -utest1 -ptest1 --socket=/data1-new/app/tmp/mysql55d.sock
 mysql> status
 --------------
 /data1-new/app/services/mysql55d/bin/mysql Ver 14.14 Distrib 5.5.31, for Linux (x86_64) using readline 5.1
 Connection id:8
 Current database:
 Current user:test1@localhost
 SSL:Not in use
 Current pager:stdout
 Using outfile:''
 Using delimiter:;
 Server version:5.5.31-log Source distribution
 Protocol version:10
 Connection:Localhost via UNIX socket
 Server characterset:utf8
 Db characterset:utf8
 Client characterset:utf8
 Conn. characterset:utf8
 UNIX socket:/data1-new/app/tmp/mysql55d.sock
 Uptime:9 min 44 sec

 Threads: 1 Questions: 87 Slow queries: 4 Opens: 38 Flush tables: 2 Open tables: 2 Queries per second avg: 0.148

 mysql> select current_user(),user();
 +-----------------+-----------------+
 | current_user() | user() |
 +-----------------+-----------------+
 | test1@localhost | test1@localhost |
 +-----------------+-----------------+
 1 row in set (0.00 sec)

2 localhost的登录协议

 On Unix, MySQL programs treat the host name localhost specially, in a way that is likely different from what you expect compared to other network-based programs. For connections to localhost, MySQL programs attempt to connect to the local server by using a Unix socket file. This occurs even if a --port or -P option is given to specify a port number. To ensure that the client makes a TCP/IP connection to the local server, use --host or -h to specify a host name value of 127.0.0.1, or the IP address or name of the local server. You can also specify the connection protocol explicitly, even for localhost, by using the --protocol=TCP option. For example:
 shell> mysql --host=127.0.0.1
 shell> mysql --protocol=TCP
 http://dev.mysql.com/doc/refman/5.6/en/connecting.htm

当指定-h localhost选项时，采用unix socket方式连接，

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 [root@mysqlslave3 ~]# strace /data1/app/services/mysql55a/bin/mysql --socket=/data1/app/tmp/mysql55a.sock -hlocalhost -utest1 -ptest1
 execve("/data1/app/services/mysql55a/bin/mysql", ["/data1/app/services/mysql55a/bin"..., "--socket=/data1/app/tmp/mysql55a"..., "-hlocalhost", "-utest1", "-ptest1", "-o", "/tmp/tmp12.log"], [/* 30 vars */]) = 0
 ......
 stat("/etc/my.cnf", 0x7ffeb7006980) = -1 ENOENT (No such file or directory)
 stat("/etc/mysql/my.cnf", 0x7ffeb7006980) = -1 ENOENT (No such file or directory)
 stat("/data1/app/services/mysql55/etc/my.cnf", 0x7ffeb7006980) = -1 ENOENT (No such file or directory)
 stat("/root/.my.cnf", 0x7ffeb7006980) = -1 ENOENT (No such file or directory)
 socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
 connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
 close(3) = 0
 socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
 connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
 close(3) = 0
 ......
 socket(PF_LOCAL, SOCK_STREAM, 0) = 3
 fcntl(3, F_SETFL, O_RDONLY) = 0
 fcntl(3, F_GETFL) = 0x2 (flags O_RDWR)
 connect(3, {sa_family=AF_LOCAL, sun_path="/data1/app/tmp/mysql55a.sock"}, 110) = 0
 setsockopt(3, SOL_SOCKET, SO_RCVTIMEO, "\2003\341\1\0\0\0\0\0\0\0\0\0\0\0\0", 16) = 0
 setsockopt(3, SOL_SOCKET, SO_SNDTIMEO, "\2003\341\1\0\0\0\0\0\0\0\0\0\0\0\0", 16) = 0
 setsockopt(3, SOL_IP, IP_TOS, [8], 4) = -1 EOPNOTSUPP (Operation not supported)
 setsockopt(3, SOL_SOCKET, SO_KEEPALIVE, [1], 4) = 0
 read(3, "N\0\0\0\n5.5.31-log\0\372f\25\0rvz&Gs04\0\377\367!"..., 16384) = 82
 open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 4
 fstat(4, {st_mode=S_IFREG|0644, st_size=106065056, ...}) = 0
 mmap(NULL, 106065056, PROT_READ, MAP_PRIVATE, 4, 0) = 0x7f21b9ad9000
 close(4) = 0
 stat("/data1/app/services/mysql55/share/charsets/Index.xml", 0x7ffeb7006100) = -1 ENOENT (No such file or directory)
 futex(0x90d540, FUTEX_WAKE_PRIVATE, 2147483647) = 0
 write(3, "`\0\0\1\215\246\17\0\0\0\0\1!\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 100) = 100
 read(3, "I\0\0\2\377\25\4#28000Access denied for u"..., 16384) = 77
 shutdown(3, SHUT_RDWR) = 0
 close(3) = 0
 fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 2), ...}) = 0
 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f21c8956000
 write(2, "ERROR 1045 (28000): ", 20ERROR 1045 (28000): ) = 20
 write(2, "Access denied for user 'test1'@'"..., 64Access denied for user 'test1'@'localhost' (using password: YES)) = 64
 write(2, "\n", 1
 ) = 1
 write(1, "\7", 1) = 1
 gettimeofday({1436522608, 908777}, NULL) = 0
 exit_group(1) = ?

采用TCP/IP协议连接

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 [root@mysqlslave3 ~]# strace /data1/app/services/mysql55a/bin/mysql -h127.0.0.1 -utest1 -ptest1
 execve("/data1/app/services/mysql55a/bin/mysql", ["/data1/app/services/mysql55a/bin"..., "-h127.0.0.1", "-utest1", "-ptest1"], [/* 30 vars */]) = 0
 ......
 socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
 connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
 close(3) = 0
 socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
 connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
 close(3) = 0
 ......
 socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 3
 connect(3, {sa_family=AF_INET, sin_port=htons(3306), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
 fcntl(3, F_SETFL, O_RDONLY) = 0
 fcntl(3, F_GETFL) = 0x2 (flags O_RDWR)
 setsockopt(3, SOL_SOCKET, SO_RCVTIMEO, "\2003\341\1\0\0\0\0\0\0\0\0\0\0\0\0", 16) = 0
 setsockopt(3, SOL_SOCKET, SO_SNDTIMEO, "\2003\341\1\0\0\0\0\0\0\0\0\0\0\0\0", 16) = 0
 setsockopt(3, SOL_IP, IP_TOS, [8], 4) = 0
 setsockopt(3, SOL_TCP, TCP_NODELAY, [1], 4) = 0
 setsockopt(3, SOL_SOCKET, SO_KEEPALIVE, [1], 4) = 0
 read(3, "N\0\0\0\n5.5.31-log\0\7g\25\0r2>$6$PH\0\377\367!"..., 16384) = 82
 ......
 poll([{fd=3, events=POLLIN|POLLPRI}], 1, 0) = 0 (Timeout)
 write(3, "!\0\0\0\3select @@version_comment li"..., 37) = 37
 read(3, "\1\0\0\1\1'\0\0\2\3def\0\0\0\21@@version_comme"..., 16384) = 90
 write(1, "Your MySQL connection id is 1402"..., 83Your MySQL connection id is 1402631
 Server version: 5.5.31-log Source distribution
 ) = 83
 ......

我们再看一下分别通过unix socket和TCP/IP连接数据库时，mysqld都做了什么事情

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 [root@mysqlslave3 ~]# strace -p 23465
 [root@mysqlslave3 ~]# /data1-new/app/services/mysql55d/bin/mysql -uroot -p -h127.0.0.1 -P3309
 Process 23465 attached
 restart_syscall(<... resuming interrupted call ...>) = 1
 fcntl(14, F_GETFL) = 0x2 (flags O_RDWR)
 fcntl(14, F_SETFL, O_RDWR|O_NONBLOCK) = 0
 accept(14, {sa_family=AF_INET, sin_port=htons(6771), sin_addr=inet_addr("127.0.0.1")}, [16]) = 17
 fcntl(14, F_SETFL, O_RDWR) = 0
 getsockname(17, {sa_family=AF_INET, sin_port=htons(3309), sin_addr=inet_addr("127.0.0.1")}, [16]) = 0
 fcntl(17, F_SETFL, O_RDONLY) = 0
 fcntl(17, F_GETFL) = 0x2 (flags O_RDWR)
 setsockopt(17, SOL_SOCKET, SO_RCVTIMEO, "\36\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 16) = 0
 setsockopt(17, SOL_SOCKET, SO_SNDTIMEO, ", 16) = 0
 fcntl(17, F_SETFL, O_RDWR|O_NONBLOCK) = 0
 setsockopt(17, SOL_IP, IP_TOS, [8], 4) = 0
 setsockopt(17, SOL_TCP, TCP_NODELAY, [1], 4) = 0
 futex(0xf444a4, FUTEX_WAKE_OP_PRIVATE, 1, 1, 0xf444a0, {FUTEX_OP_SET, 0, FUTEX_OP_CMP_GT, 1}) = 1
 futex(0xf438c0, FUTEX_WAKE_PRIVATE, 1) = 1
 poll([{fd=14, events=POLLIN}, {fd=16, events=POLLIN}], 2, 4294967295


 [root@mysqlslave3 ~]# strace -p 23465
 [root@mysqlslave3 ~]# /data1-new/app/services/mysql55d/bin/mysql --socket=/data1-new/app/tmp/mysql55d.sock -uroot -P3309
 Process 23465 attached
 restart_syscall(<... resuming interrupted call ...>) = 1
 fcntl(16, F_GETFL) = 0x2 (flags O_RDWR)
 fcntl(16, F_SETFL, O_RDWR|O_NONBLOCK) = 0
 accept(16, {sa_family=AF_LOCAL, NULL}, [2]) = 17
 fcntl(16, F_SETFL, O_RDWR) = 0
 getsockname(17, {sa_family=AF_LOCAL, sun_path="/data1-new/app/tmp/mysql55d.sock"}, [35]) = 0
 fcntl(17, F_SETFL, O_RDONLY) = 0
 fcntl(17, F_GETFL) = 0x2 (flags O_RDWR)
 setsockopt(17, SOL_SOCKET, SO_RCVTIMEO, "\36\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 16) = 0
 setsockopt(17, SOL_SOCKET, SO_SNDTIMEO, ", 16) = 0
 fcntl(17, F_SETFL, O_RDWR|O_NONBLOCK) = 0
 setsockopt(17, SOL_IP, IP_TOS, [8], 4) = -1 EOPNOTSUPP (Operation not supported)
 futex(0xf444a4, FUTEX_WAKE_OP_PRIVATE, 1, 1, 0xf444a0, {FUTEX_OP_SET, 0, FUTEX_OP_CMP_GT, 1}) = 1
 futex(0xf438c0, FUTEX_WAKE_PRIVATE, 1) = 1
 poll([{fd=14, events=POLLIN}, {fd=16, events=POLLIN}], 2, 4294967295

3 Unix socket VS IP socket
https://lists.freebsd.org/pipermail/freebsd-performance/2005-February/001143.html  
1 UNIX domain sockets use the file system as the address name space.

2 UNIX domain sockets have explicit knowledge that they're executing on

  the same system.  They avoid the extra context switch through the

  netisr, and a sending thread will write the stream or datagrams directly

  into the receiving socket buffer.  No checksums are calculated, no

  headers are inserted, no routing is performed, etc.

3 In general, the argument for implementing over TCP is that it gives you

location independence and immediate portability -- you can move the client

or the daemon, update an address, and it will "just work".  The sockets

layer provides a reasonable abstraction of communications services, so

it's not hard to write an application so that the connection/binding

portion knows about TCP and UNIX domain sockets, and all the rest just

uses the socket it's given.  So if you're looking for performance locally,

I think UNIX domain sockets probably best meet your need.  Many people

will code to TCP anyway because performance is often less critical, and

the network portability benefit is substantial.

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