Provided by: login_4.2-3.1ubuntu5_amd64 
名称
login - 在系统上启动回话
大纲
login [-p] [-h 主机] [用户名] [ENV=VAR...]
login [-p] [-h 主机] -f 用户名
login [-p] -r 主机
描述
The login program is used to establish a new session with the system. It is normally
invoked automatically by responding to the login: prompt on the user's terminal. login
may be special to the shell and may not be invoked as a sub-process. When called from a
shell, login should be executed as exec login which will cause the user to exit from the
current shell (and thus will prevent the new logged in user to return to the session of
the caller). Attempting to execute login from any shell but the login shell will produce
an error message.
The user is then prompted for a password, where appropriate. Echoing is disabled to
prevent revealing the password. Only a small number of password failures are permitted
before login exits and the communications link is severed.
If password aging has been enabled for your account, you may be prompted for a new
password before proceeding. You will be forced to provide your old password and the new
password before continuing. Please refer to passwd(1) for more information.
Your user and group ID will be set according to their values in the /etc/passwd file. The
value for $HOME, $SHELL, $PATH, $LOGNAME, and $MAIL are set according to the appropriate
fields in the password entry. Ulimit, umask and nice values may also be set according to
entries in the GECOS field.
On some installations, the environmental variable $TERM will be initialized to the
terminal type on your tty line, as specified in /etc/ttytype.
命令解释器的初始化脚本也可能执行。请参考手册中相应的章节来获取关于此功能的更多信息。
在登录 shell
中以第一个字符是“*”标注的是子系统登录。给定的主目录将被用于用户实际登录的新文件系统的根。
The login program is NOT responsible for removing users from the utmp file. It is the
responsibility of getty(8) and init(8) to clean up apparent ownership of a terminal
session. If you use login from the shell prompt without exec, the user you use will
continue to appear to be logged in even after you log out of the "subsession".
选项
-f
不要执行认证，用户已经预认证过。
注意：此时，username 是强制的。
-h
此登录的远程主机名。
-p
保留环境。
-r
为 rlogin (远程登录)执行 autologin (自动登录)协议。
-r, -h and -f 只能用于 root 使用 login 时。
CAVEATS
此版本的 login 有很多编译选项，只有一部分可以在任何站点使用。
文件的位置由系统配置决定。
The login program is NOT responsible for removing users from the utmp file. It is the
responsibility of getty(8) and init(8) to clean up apparent ownership of a terminal
session. If you use login from the shell prompt without exec, the user you use will
continue to appear to be logged in even after you log out of the "subsession".
As with any program, login's appearance can be faked. If non-trusted users have physical
access to a machine, an attacker could use this to obtain the password of the next person
coming to sit in front of the machine. Under Linux, the SAK mechanism can be used by users
to initiate a trusted path and prevent this kind of attack.
配置文件
在 /etc/login.defs 中有如下配置变量，可以用来更改此工具的行为：
CONSOLE_GROUPS (string)
在控制台登录时，添加到用户附加组集中的组列表(就如 CONSOLE 所确定的)。默认是无。
使用时需要注意：这可能使用户获取这些组的永久权限，甚至登录到的不是此控制台时。
DEFAULT_HOME (boolean)
如果不能 cd 到主目录时，说明是否允许登录。默认是否。
如果设置为 yes，如果不能 cd 到主目录时，用户将会登录到根目录(/)。
ENV_PATH (string)
If set, it will be used to define the PATH environment variable when a regular user
login. The value is a colon separated list of paths (for example /bin:/usr/bin) and
can be preceded by PATH=. The default value is PATH=/bin:/usr/bin.
ENV_SUPATH (string)
If set, it will be used to define the PATH environment variable when the superuser
login. The value is a colon separated list of paths (for example
/sbin:/bin:/usr/sbin:/usr/bin) and can be preceded by PATH=. The default value is
PATH=/sbin:/bin:/usr/sbin:/usr/bin.
ERASECHAR (number)
终端擦除字符 (010 = backspace, 0177 = DEL)。
此值可以使用前缀“0”表示八进制，“0x”表示十六进制。
FAIL_DELAY (number)
登录失败后，等待多少秒才再允许登录。
FAKE_SHELL (string)
如果设置了，login 将执行此 shell 而不是在 /etc/passwd 中指定的用户 shell。
HUSHLOGIN_FILE (string)
If defined, this file can inhibit all the usual chatter during the login sequence. If
a full pathname is specified, then hushed mode will be enabled if the user's name or
shell are found in the file. If not a full pathname, then hushed mode will be enabled
if the file exists in the user's home directory.
KILLCHAR (number)
终端 KILL 字符 (025 = CTRL/U)。
此值可以使用前缀“0”表示八进制，“0x”表示十六进制。
LOGIN_RETRIES (number)
密码错误时，重试的最大次数。
This will most likely be overridden by PAM, since the default pam_unix module has its
own built in of 3 retries. However, this is a safe fallback in case you are using an
authentication module that does not enforce PAM_MAXTRIES.
LOGIN_TIMEOUT (number)
最大登录时间(以秒为单位)。
LOG_OK_LOGINS (boolean)
允许记录成功登录。
LOG_UNKFAIL_ENAB (boolean)
在记录到登录失败时，允许记录未知用户名。
注意：如果用户不小心将密码输入到了登录名中，记录未知用户名可能是一个安全隐患。
TTYGROUP (string), TTYPERM (string)
The terminal permissions: the login tty will be owned by the TTYGROUP group, and the
permissions will be set to TTYPERM.
By default, the ownership of the terminal is set to the user's primary group and the
permissions are set to 0600.
TTYGROUP can be either the name of a group or a numeric group identifier.
If you have a write program which is "setgid" to a special group which owns the
terminals, define TTYGROUP to the group number and TTYPERM to 0620. Otherwise leave
TTYGROUP commented out and assign TTYPERM to either 622 or 600.
TTYTYPE_FILE (string)
If defined, file which maps tty line to TERM environment parameter. Each line of the
file is in a format something like "vt100 tty01".
USERGROUPS_ENAB (boolean)
如果设置为 yes，如果组中没有成员了，userdel 将移除此用户组，useradd
创建用户时，也会创建一个同名的默认组。
文件
/var/run/utmp
当前登录会话的列表。
/var/log/wtmp
先前的登录会话列表。
/etc/passwd
用户账户信息。
/etc/shadow
安全用户账户信息。
/etc/motd
System message of the day file.
/etc/nologin
阻止非 root 用户登录。
/etc/ttytype
终端类型列表。
$HOME/.hushlogin
阻止现实系统信息。
/etc/login.defs
Shadow 密码套件配置。
参见
mail(1), passwd(1), sh(1), su(1), login.defs(5), nologin(5), passwd(5), securetty(5),
getty(8).