今天了解了一下 sudo 的配置，然后对于第二列等号左边的 hostname 配置很疑惑，这个有什么用？
不是所有登陆主机的人的 hostname 都是固定的吗？
虽然可以修改这个值。但是这个限制到底有什么意义？
是用在什么场合下的？？
你以为你了解了，其实是心急了。答案都在 /usr/share/doc /usr/share/man 里面
Groups of machines. You may prefer to use hostnames (perhaps using
wildcards for entire domains) or IP addresses instead.
Host_Alias FILESERVERS = fs1, fs2
Host_Alias MAILSERVERS = smtp, smtp2
/>Host alias specification
/>Host_Alias SPARC = bigtime, eclipse, moet, anchor:\
SGI = grolsch, dandelion, black:\
ALPHA = widget, thalamus, foobar:\
HPPA = boa, nag, python
Host_Alias CUNETS = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = master, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules

/>User specification
root and users in group wheel can run anything on any machine as any user
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
full time sysadmins can run anything on any machine without a password
FULLTIMERS ALL = NOPASSWD: ALL
part time sysadmins may run anything but need a password
PARTTIMERS ALL = ALL
jack may run anything on machines in CSNETS
jack CSNETS = ALL
lisa may run any command on any host in CUNETS (a class B network)
lisa CUNETS = ALL
operator may run maintenance commands and anything in /usr/oper/bin/
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
joe may su only to operator
joe ALL = /usr/bin/su operator
pete may change passwords for anyone but root on the hp snakes
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd *root*
bob may run anything on the sparc and sgi machines as any user
listed in the Runas_Alias "OP" (ie: root and operator)
bob SPARC = (OP) ALL : SGI = (OP) ALL
jim may run anything on machines in the biglab netgroup
jim +biglab = ALL
users in the secretaries netgroup need to help manage the printers
as well as add and remove users
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
fred can run commands as oracle or sybase without a password
fred ALL = (DB) NOPASSWD: ALL
on the alphas, john may su to anyone but root and flags are not allowed
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
jen can run anything on all machines except the ones
in the "SERVERS" Host_Alias
jen ALL, !SERVERS = ALL
jill can run any commands in the directory /usr/bin/, except for
those in the SU and SHELLS aliases.
jill SERVERS = /usr/bin/, !SU, !SHELLS
steve can run any command in the directory /usr/local/op_commands/
as user operator.
steve CSNETS = (operator) /usr/local/op_commands/
matt needs to be able to kill things on his workstation when
they get hung.
matt valkyrie = KILL
users in the WEBMASTERS User_Alias (will, wendy, and wim)
may run any command as user www (which owns the web pages)
or simply su to www.
WEBMASTERS www = (www) ALL, (root) /usr/bin/su www
anyone can mount/unmount a cd-rom on the machines in the CDROM alias
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM


可我还是不明白 这个主机名 比如你贴出来的例子里的 www 这些主机名是什么含义？ 哪里来的？
为什么一个系统会有多个主机名?

你可以自己试试 https://tools.ietf.org/html/rfc1178
“这些主机名是什么含义？ 哪里来的？为什么一个系统会有多个主机名?”
为什么你要有网名姓名小名外号绰号学号工号身份证号护照号？大家说话都用“你”不行吗？或者说给自己起几十个外号行吗？顺其自然

比如你贴出来的例子里的 www 这些主机名是什么含义？
没有含义
看站长的这贴 https://www.v2ex.com/t/74166
www 名 name，v2ex.com 域 domain。dns 域名系统 domain name system。

参考 https://unix.stackexchange.com/questions/71684/the-host-variable-in-etc-sudoers，hostname 是给“一个 sudoers 文件给很多台机器用”这种情况设计的，各个机器只会应用适用于自己的主机名的规则。这样如果很多服务器要用同一套 sudo 规则的话，管理起来方便一点。楼上的回复也是 [doge]

谢了哈，嗯，看起来是这么回事啊，居然就是为了这个。。。。

谢谢哈，是我没有描述清楚了。