Linux-PAM认证模块

用户访问服务器的时候，服务器的某一个服务程序把用户的谁请求发送到PAM模块进行认证。对于不同的服务器应用程序所对应的PAM模块也是不同的。如果想查看某个程序是否支持PAM认证，可以用ldd命令进行检查：

例如：查看sshd是不是支持ＰＡＭ模块认证：

由于在程序模块里链接了libpam.so.0 =< /lib/libpam.so.0 ,说明此程序可以进行ＰＡＭ认证。

当一个服务器请求PAM模块的时候，ＰＡＭ本身是不提供服务验证的，它是调用其它的一群模块来进行服务器请求验证，这样的文件全放在了/lib/security中。具体到哪一个服务使用哪一种具体的模块，这是由具体的ＰＡＭ服务文件定义的（/etc/pam.d/）.

[root@localhost root]# ls /etc/pam.d/
authconfig      neat                      redhat-config-network        su
chfn            other                       redhat-config-network-cmd    sudo
chsh            passwd                    redhat-config-network-druid  system-auth
halt            poweroff                   rhn_register                 up2date
internet-druid  ppp                       setup                        up2date-config
kbdrate         reboot                    smtp                         up2date-nox
login           redhat-config-mouse   sshd

PAM服务文件

１、# more /etc/pam.d/login 
auth       required     pam_securetty.so
auth       required     pam_stack.so service=system-auth
auth       required     pam_nologin.so
account    required     pam_stack.so service=system-auth
password   required     pam_stack.so service=system-auth
session    required     pam_stack.so service=system-auth
session    optional     pam_console.so

PAM服务文件的格式（四部分）

①、auth              required        pam_securety.so
②、auth              required        pam_stack.so         service=system-auth
③、auth              required        pam_nologin.so

[root@localhost root]# cd /etc/pam.d/
[root@localhost pam.d]# more login
#%PAM-1.0
auth       required     pam_securetty.so
auth       required     pam_stack.so service=system-auth
auth       required     pam_nologin.so
account    required     pam_stack.so service=system-auth
password   required     pam_stack.so service=system-auth
session    required     pam_stack.so service=system-auth
session    optional     pam_console.so
[root@localhost pam.d]# cd /usr/share/doc/pam-0.75/txts/
[root@localhost txts]# ls
pam_appl.txt               README.pam_ftp          README.pam_shells
pam_modules.txt          README.pam_limits       README.pam_stack
pam.txt                      README.pam_listfile      README.pam_stress
README                     README.pam_localuser   README.pam_tally
README.pam_access    README.pam_mail         README.pam_time
README.pam_chroot    README.pam_nologin     README.pam_timestamp
README.pam_console   README.pam_permit      README.pam_unix
README.pam_cracklib   README.pam_pwdb       README.pam_userdb
README.pam_deny      README.pam_rhosts      README.pam_warn
README.pam_env        README.pam_rootok     README.pam_wheel
README.pam_filter      README.pam_securetty  README.pam_xauth
[root@localhost txts]# more README.pam_securetty
pam_securetty:
        Allows root logins only if the user is logging in on a
        "secure" tty, as defined by the listing in /etc/securetty

        Also checks to make sure that /etc/securetty is a plain
        file and not world writable.

        - Elliot Lee , Red Hat Software.
                July 25, 1996.
[root@localhost txts]# more /etc/securetty
console
vc/1
vc/2
vc/3
vc/4
vc/5
vc/6
vc/7
vc/8
vc/9
vc/10
vc/11
tty1
tty2
tty3
tty4
tty5
tty6
tty7
tty8
tty9
tty10
tty11
[root@localhost txts]# more /etc/pam.d/system-auth
#%PAM-1.0
# This file is auto-generated.
# User changes will be destroyed the next time authconfig is run.
auth        required      /lib/security/$ISA/pam_env.so
auth        sufficient    /lib/security/$ISA/pam_unix.so likeauth nullok
auth        required      /lib/security/$ISA/pam_deny.so

account     required      /lib/security/$ISA/pam_unix.so

password    required      /lib/security/$ISA/pam_cracklib.so retry=3 type=
password    sufficient    /lib/security/$ISA/pam_unix.so nullok use_authtok md5 shadow
password    required      /lib/security/$ISA/pam_deny.so

session     required      /lib/security/$ISA/pam_limits.so
session     required      /lib/security/$ISA/pam_unix.so
[root@localhost txts]# pwd
/usr/share/doc/pam-0.75/txts
[root@localhost txts]# more README.pam_nologin
# $Id: README,v 1.1.1.1 2000/06/20 22:11:46 agmorgan Exp $
#

This module always lets root in; it lets other users in only if the file
/etc/nologin doesn‘t exist.  In any case, if /etc/nologin exists, it‘s
contents are displayed to the user.

module services provided:

        auth            _authentication and _setcred (blank)

Michael K. Johnson
[root@localhost txts]# touch /etc/nologin
[root@localhost txts]# useradd leekwen
[root@localhost txts]# passwd leekwen
Changing password for user leekwen.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
[root@localhost txts]# ssh [email protected]
[email protected]‘s password:
Permission denied, please try again.
[email protected]‘s password:
Permission denied, please try again.
[email protected]‘s password:
Permission denied (publickey,password,keyboard-interactive).
[root@localhost txts]# rm /etc/nologin
rm: remove regular empty file `/etc/nologin‘? y
[root@localhost txts]# ssh [email protected]
[email protected]‘s password:
[leekwen@localhost leekwen]$ pwd
/home/leekwen
[leekwen@localhost leekwen]$ exit
logout
Connection to 192.168.0.188 closed.
[root@localhost txts]# cd /etc/pam.d/
[root@localhost pam.d]# more login
#%PAM-1.0
auth       required     pam_securetty.so
auth       required     pam_stack.so service=system-auth
auth       required     pam_nologin.so
account    required     pam_stack.so service=system-auth
password   required     pam_stack.so service=system-auth
session    required     pam_stack.so service=system-auth
session    optional     pam_console.so 
[root@localhost pam.d]# tty
/dev/pts/2
[root@localhost pam.d]# ls /dev/tty1
/dev/tty1