改变用户默认shell

查看用户当前shell。
bigfish@wangyu-desktop:~ $ echo $SHELL             
/bin/bash

/etc/passwd记录着用户的一些信息，其中最后是用户默认的shell。
bigfish@wangyu-desktop:~ $ cat /etc/passwd
root:x:0:0:root:/root:/bin/sh
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/bin/sh
man:x:6:12:man:/var/cache/man:/bin/sh
lp:x:7:7:lp:/var/spool/lpd:/bin/sh
mail:x:8:8:mail:/var/mail:/bin/sh
news:x:9:9:news:/var/spool/news:/bin/sh
uucp:x:10:10:uucp:/var/spool/uucp:/bin/sh
proxy:x:13:13:proxy:/bin:/bin/sh
www-data:x:33:33:www-data:/var/www:/bin/sh
backup:x:34:34:backup:/var/backups:/bin/sh
list:x:38:38:Mailing List Manager:/var/list:/bin/sh
irc:x:39:39:ircd:/var/run/ircd:/bin/sh
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh
nobody:x:65534:65534:nobody:/nonexistent:/bin/sh
libuuid:x:100:101::/var/lib/libuuid:/bin/sh
dhcp:x:101:102::/nonexistent:/bin/false
syslog:x:102:103::/home/syslog:/bin/false
klog:x:103:104::/home/klog:/bin/false
hplip:x:104:7:HPLIP system user,,,:/var/run/hplip:/bin/false
avahi-autoipd:x:105:113:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false
gdm:x:106:114:Gnome Display Manager:/var/lib/gdm:/bin/false
pulse:x:107:116:PulseAudio daemon,,,:/var/run/pulse:/bin/false
messagebus:x:108:119::/var/run/dbus:/bin/false
avahi:x:109:120:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false
polkituser:x:110:122:PolicyKit,,,:/var/run/PolicyKit:/bin/false
haldaemon:x:111:123:Hardware abstraction layer,,,:/var/run/hald:/bin/false
Debian-exim:x:112:124::/var/spool/exim4:/bin/false
sshd:x:113:65534::/var/run/sshd:/usr/sbin/nologin
bigfish:x:1002:1002:bigfish,,,,:/home/bigfish:/bin/bash  //这里的用户是我注册的
tftpd:x:1003:65534::/home/tftpd:/bin/false


usermod -s 指定shell  指定用户
bigfish@wangyu-desktop:~ $ sudo usermod -s /bin/sh bigfish
[sudo] password for bigfish:

再次查看/etc/passwd文件，查看是否默认shell已经修改成我所需要的。
bigfish@wangyu-desktop:~ $ cat /etc/passwd
root:x:0:0:root:/root:/bin/sh
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/bin/sh
man:x:6:12:man:/var/cache/man:/bin/sh
lp:x:7:7:lp:/var/spool/lpd:/bin/sh
mail:x:8:8:mail:/var/mail:/bin/sh
news:x:9:9:news:/var/spool/news:/bin/sh
uucp:x:10:10:uucp:/var/spool/uucp:/bin/sh
proxy:x:13:13:proxy:/bin:/bin/sh
www-data:x:33:33:www-data:/var/www:/bin/sh
backup:x:34:34:backup:/var/backups:/bin/sh
list:x:38:38:Mailing List Manager:/var/list:/bin/sh
irc:x:39:39:ircd:/var/run/ircd:/bin/sh
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh
nobody:x:65534:65534:nobody:/nonexistent:/bin/sh
libuuid:x:100:101::/var/lib/libuuid:/bin/sh
dhcp:x:101:102::/nonexistent:/bin/false
syslog:x:102:103::/home/syslog:/bin/false
klog:x:103:104::/home/klog:/bin/false
hplip:x:104:7:HPLIP system user,,,:/var/run/hplip:/bin/false
avahi-autoipd:x:105:113:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false
gdm:x:106:114:Gnome Display Manager:/var/lib/gdm:/bin/false
pulse:x:107:116:PulseAudio daemon,,,:/var/run/pulse:/bin/false
messagebus:x:108:119::/var/run/dbus:/bin/false
avahi:x:109:120:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false
polkituser:x:110:122:PolicyKit,,,:/var/run/PolicyKit:/bin/false
haldaemon:x:111:123:Hardware abstraction layer,,,:/var/run/hald:/bin/false
Debian-exim:x:112:124::/var/spool/exim4:/bin/false
sshd:x:113:65534::/var/run/sshd:/usr/sbin/nologin
bigfish:x:1002:1002:bigfish,,,,:/home/bigfish:/bin/sh  已经修改成/bin/sh
tftpd:x:1003:65534::/home/tftpd:/bin/false
bigfish@wangyu-desktop:~ $