systemd

meson.build文件中有这么一段。最后会将progs的第一个元素转换成大写：prog[0].to_upper()；这个是将其转换为宏定义。在程序使用时使用比如：static const char* const sulogin_cmdline[] = {SULOGIN, NULL}; ；这个会为代码阅读搜索带来麻烦。

# if -Dxxx-path option is found, use that. Otherwise, check in $PATH,
# /usr/sbin, /sbin, and fall back to the default from middle column.
progs = [['quotaon',    '/usr/sbin/quotaon'    ],
         ['quotacheck', '/usr/sbin/quotacheck' ],
         ['kmod',       '/usr/bin/kmod'        ],
         ['kexec',      '/usr/sbin/kexec'      ],
         ['sulogin',    '/usr/sbin/sulogin'    ],
         ['mount',      '/usr/bin/mount',      'MOUNT_PATH'],
         ['umount',     '/usr/bin/umount',     'UMOUNT_PATH'],
         ['loadkeys',   '/usr/bin/loadkeys',   'KBD_LOADKEYS'],
         ['setfont',    '/usr/bin/setfont',    'KBD_SETFONT'],
        ]
foreach prog : progs
        path = get_option(prog[0] + '-path')
        if path != ''
                message('Using @1@ for @0@'.format(prog[0], path))
        else
                exe = find_program(prog[0],
                                   '/usr/sbin/' + prog[0],
                                   '/sbin/' + prog[0],
                                   required: false)
                path = exe.found() ? exe.path() : prog[1]
        endif
        name = prog.length() > 2 ? prog[2] : prog[0].to_upper()
        conf.set_quoted(name, path)
        substs.set(name, path)
endforeach

sulogin

sulogin - single-user login
用法：sulogin [options] [tty]
如果系统进入单用户模式时（比如进入emergency mode），由init、systemd 带起来sulogin。
会提示用户输入密码，进入系统维护窗口（或者键入Ctrl-D，继续正常的启动，就不会进入单用户，紧急模式）。

如果root用户被锁定，并且带有选项：–force，不需要密码就可以之间进入系统。
sulogin will be connected to the current terminal, or to the optional tty device that can be specified on the command line (typically /dev/console).

When the user exits from the single-user shell, or presses control-D at the prompt, the system will continue to boot.

选项

-e, --force If the default method of obtaining the root password from the system via getpwnam(3) fails, then examine /etc/passwd and /etc/shadow to get the password. If these files are damaged or nonexistent, or when root account is locked by ‘!’ or ‘*’ at the begin of the password then sulogin will start a root shell without asking for a password. Only use the -e option if you are sure the console is physically protected against unauthorized access.
-p, --login-shell Specifying this option causes sulogin to start the shell process as a login shell.
-t, --timeout seconds Specify the maximum amount of time to wait for user input. By default, sulogin will wait forever.
-h, --help Display help text and exit.
-V, --version Display version information and exit.

环境变量

使用到的环境变量是：SUSHELL or sushell，指明要启动什么shell。If the environment variable is not set, it will try to execute root’s shell from /etc/passwd. If that fails, it will fall back to /bin/sh.
https://www.kernel.org/pub/linux/utils/util-linux/

sulogin 编译选项

[root@10 ~]# rpm -q --queryformat=“%{NAME}: %{OPTFLAGS}\n” util-linux-2.32.1-35.el8.x86_64
util-linux: -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection