谁能解读一下/etc/passwd文件？

[relaxssl]

vi /etc/passwd
输出下面引用部分， 以www-data33:33:www-data:/var/www:/bin/sh为例子， 谁来解读一下各部分代表的意义并举例说明实际应用。

root0:0:root:/root:/bin/bash
daemon1:1:daemon:/usr/sbin:/bin/sh
bin2:2:bin:/bin:/bin/sh
sys3:3:sys:/dev:/bin/sh
sync4:65534:sync:/bin:/bin/sync
games5:60:games:/usr/games:/bin/sh
man6:12/var/cache/man:/bin/sh
lp7:7:lp:/var/spool/lpd:/bin/sh
mail8:8:mail:/var/mail:/bin/sh
news9:9:news:/var/spool/news:/bin/sh
uucp10:10:uucp:/var/spool/uucp:/bin/sh
proxy13:13:proxy:/bin:/bin/sh
www-data33:33:www-data:/var/www:/bin/sh
backup34:34:backup:/var/backups:/bin/sh
list38:38:Mailing List Manager:/var/list:/bin/sh
irc39:39:ircd:/var/run/ircd:/bin/sh
gnats41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh
nobody65534:65534:nobody:/nonexistent:/bin/sh
libuuid100:101::/var/lib/libuuid:/bin/sh
syslog101:103::/home/syslog:/bin/false
mysql102:105:MySQL Server,,,:/var/lib/mysql:/bin/false
landscape103:106::/var/lib/landscape:/bin/false
linux1000:1000:linux,,,:/home/linux:/bin/bash
messagebus104:114::/var/run/dbus:/bin/false
haldaemon105:115:Hardware abstraction layer,,,:/var/run/hald:/bin/false
pulse106:116:PulseAudio daemon,,,:/var/run/pulse:/bin/false
gdm107:118:Gnome Display Manager:/var/lib/gdm:/bin/false
sshd108:65534::/var/run/sshd:/usr/sbin/nologin
citadel109:119:Citadel system user,,,:/var/lib/citadel:/bin/false

[O_O_BOT]

irc <lolicon> say: man passwd

[O_O_BOT]

irc <lolicon> say: man 5 passwd

[O_O_BOT]

irc <liyingqiao> say: 手机水一下，passwd