su: Do not change directory/set variables by default, instead add a --login option

apps/login.cpp

@@ -38,7 +38,7 @@ Result<int> luna_main(int argc, char** argv)
         username = name.view();
     }
 
-    execl("/bin/su", "login", "-p", "--", username.chars(), nullptr);
+    execl("/bin/su", "login", "-lp", "--", username.chars(), nullptr);
 
     perror("su");
     return 1;

apps/sh.cpp

@@ -71,12 +71,9 @@ Result<int> luna_main(int argc, char** argv)
 
         if (getuid() == 0) prompt_end = '#';
 
-        username = getenv("USER");
-        if (!username)
-        {
         struct passwd* pw = getpwuid(getuid());
         if (pw) { username = pw->pw_name; }
-        }
+        else { username = getenv("USER"); }
     }
 
     while (1)

apps/su.cpp

@@ -55,6 +55,7 @@ Result<int> luna_main(int argc, char** argv)
 {
     StringView name;
     bool prompt_password;
+    bool login;
 
     if (geteuid() != 0)
     {
@@ -67,6 +68,7 @@ Result<int> luna_main(int argc, char** argv)
     parser.add_system_program_info("su"_sv);
     parser.add_positional_argument(name, "name"_sv, "root"_sv);
     parser.add_switch_argument(prompt_password, 'p', "prompt", "prompt for a password even if running as root");
+    parser.add_switch_argument(login, 'l', "login"_sv, "change directory to the user's home and start a login shell");
     parser.parse(argc, argv);
 
     struct passwd* entry = getpwnam(name.chars());
@@ -93,10 +95,16 @@ Result<int> luna_main(int argc, char** argv)
     setgid(entry->pw_gid);
     setuid(entry->pw_uid);
 
+    if (login)
+    {
         chdir(entry->pw_dir);
+        clearenv();
+        setenv("PATH", "/bin:/sbin", 1);
+    }
+
+    if (login || entry->pw_uid != 0) setenv("USER", entry->pw_name, 1);
 
     setenv("HOME", entry->pw_dir, 1);
-    setenv("USER", entry->pw_name, 1);
     setenv("SHELL", entry->pw_shell, 1);
 
     execl(entry->pw_shell, entry->pw_shell, NULL);

initrd/etc/init/99-login

@@ -1,4 +1,3 @@
 Name=login
 Command=/bin/login
 Restart=true
-Environment=PATH=/bin:/sbin

libc/src/env.cpp

@@ -54,10 +54,10 @@ static Result<void> _try_move_env()
 
     if (!env)
     {
+        TRY(g_dynamic_env.try_append(nullptr));
         guard.deactivate();
         env_is_dynamic = true;
         environ = g_dynamic_env.data();
-        check(!environ);
         return {};
     }
 
@@ -109,10 +109,12 @@ extern "C"
             {
                 if (element) free(element);
             }
+
+            g_dynamic_env.clear();
         }
 
-        env_is_dynamic = false;
         environ = nullptr;
+        env_is_dynamic = false;
 
         return 0;
     }