Add support for a rescue (recovery) mode from kernel cmdline

This patch adds a rescue (revovery) mode to Finit.  Simply add `rescue`
to the kernel cmdline at boot and the following steps at bootstrap will
be skipped:

- Load of services/run/task/etc in /etc/finit.conf + /etc/finit.d/*.conf
- fsck of filesystems in /etc/fstab
- Remount of / to read-write
- Mount of all filesystems in /etc/fstab
- swapon
- A few plugin hooks:
  - HOOK_ROOTFS_UP
  - HOOK_MOUNT_ERROR
  - HOOK_BASEFS_UP
- `runparts DIR`
- /etc/rc.local

Instead of loading /etc/finit.conf and /etc/finit.d/*.conf Finit loads
the file /lib/finit/rescue.conf, which can be overridden by the operator
if needed.  If this file is removed (or lost), Finit falls back to start
a simple root shell, without any login.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

configure.ac

@@ -217,6 +217,9 @@ AC_EXPAND_DIR(plugin_path, "$libdir/finit/plugins")
 AC_SUBST(plugin_path)
 AC_DEFINE_UNQUOTED(PLUGIN_PATH, "$plugin_path", [Finit plugin path])
 
+AC_EXPAND_DIR(rescue_conf, "$libdir/finit/rescue.conf")
+AC_DEFINE_UNQUOTED(RESCUE_CONF, "$rescue_conf", [Finit rescue mode .conf])
+
 # Generate all files
 AC_OUTPUT
 

doc/TODO.md

@@ -21,9 +21,6 @@ can also be used.
 General
 -------
 
-* Add support for `rescue` on the kernel command line, start rescue mode
-  if enabled with `configure` script.  Could mean skip `/etc/finit.conf`
-  et al and jump straight to a single getty login on console.
 * Add support for timed shutdown in Finit, including cancelled shutdown.
 * SysV init and systemd use SIGUSR1 to restart their FIFO/D-Bus.  Add
   API restart to SIGHUP callback for the same functionality in Finit.

src/Makefile.am

@@ -58,6 +58,7 @@ REBOOT_LNKS        = shutdown halt poweroff suspend
 
 # Hook in install to add finit and reboot symlink(s)
 install-exec-hook:
+	@$(INSTALL_DATA) $(srcdir)/rescue.conf $(DESTDIR)$(pkglibdir)
 	@for file in $(INIT_LNKS); do				\
 		lnk=$(DESTDIR)$(sbindir)/$$file;		\
 		if [ -e $$lnk ]; then				\
@@ -80,6 +81,7 @@ install-exec-hook:
 	fi
 
 uninstall-hook:
+	@$(RM) $(DESTDIR)$(pkglibdir)/rescue.conf
 	@for file in $(INIT_LNKS); do				\
 		lnk=`readlink $(DESTDIR)$(sbindir)/$$file`;	\
 		if [ "$$lnk" != "finit" ]; then			\

src/conf.c

@@ -78,6 +78,9 @@ void conf_parse_cmdline(void)
 		/* Catches finit_debug (deprecated), --debug, and debug */
 		if (strstr(tok, "debug"))
 			dbg = 1;
+
+		if (strstr(tok, "rescue") || strstr(tok, "recover"))
+			rescue = 1;
 	}
 	fclose(fp);
 
@@ -551,6 +554,19 @@ int conf_reload(void)
 	svc_mark_dynamic();
 	tty_mark();
 
+	if (rescue) {
+		int rc;
+		char line[80] = "tty [12345] @console noclear nologin";
+
+		/* If rescue.conf is missing, fall back to a root shell */
+		rc = parse_conf(RESCUE_CONF);
+		if (rc)
+			tty_register(line, global_rlimit, NULL);
+
+		print(rc, "Entering rescue mode");
+		goto done;
+	}
+
 	/* First, read /etc/finit.conf */
 	parse_conf(FINIT_CONF);
 
@@ -795,6 +811,10 @@ int conf_monitor(uev_ctx_t *ctx)
 {
 	int rc = 0;
 
+	/* Skip second run, when called from finit.c in rescue mode */
+	if (ctx && rescue)
+		return 0;
+
 	/*
 	 * If only one watcher fails, that's OK.  A user may have only
 	 * one of /etc/finit.conf or /etc/finit.d in use, and may also

src/finit.c

@@ -53,6 +53,7 @@ int   wdogpid   = 0;		/* No watchdog by default */
 int   runlevel  = 0;		/* Bootstrap 'S' */
 int   cfglevel  = RUNLEVEL;	/* Fallback if no configured runlevel */
 int   prevlevel = -1;
+int   rescue    = 0;		/* rescue mode from kernel cmdline */
 char *sdown     = NULL;
 char *network   = NULL;
 char *hostname  = NULL;
@@ -262,18 +263,20 @@ static void finalize(void)
 	/*
 	 * Network stuff
 	 */
-	_d("Setting up networking ...");
+	if (!rescue) {
-	networking();
+		_d("Setting up networking ...");
-	umask(022);
+		networking();
 
-	/* Hooks that rely on loopback, or basic networking being up. */
+		/* Hooks that rely on loopback, or basic networking being up. */
-	_d("Calling all network up hooks ...");
+		_d("Calling all network up hooks ...");
-	plugin_run_hooks(HOOK_NETWORK_UP);
+		plugin_run_hooks(HOOK_NETWORK_UP);
+	}
+	umask(022);
 
 	/*
 	 * Run startup scripts in the runparts directory, if any.
 	 */
-	if (runparts && fisdir(runparts)) {
+	if (runparts && fisdir(runparts) && !rescue) {
 		_d("Running startup scripts in %s ...", runparts);
 		run_parts(runparts, NULL);
 		if (conf_any_change())
@@ -296,7 +299,7 @@ static void finalize(void)
 	service_step_all(SVC_TYPE_ANY);
 
 	/* Convenient SysV compat for when you just don't care ... */
-	if (!access(FINIT_RC_LOCAL, X_OK)) {
+	if (!access(FINIT_RC_LOCAL, X_OK) && !rescue) {
 		run_interactive(FINIT_RC_LOCAL, "Calling %s", FINIT_RC_LOCAL);
 		if (conf_any_change())
 			service_reload_dynamic();
@@ -385,7 +388,7 @@ int main(int argc, char* argv[])
 	/*
 	 * Check file filesystems in /etc/fstab
 	 */
-	for (int pass = 1; pass < 10; pass++) {
+	for (int pass = 1; pass < 10 && !rescue; pass++) {
 		if (fsck(pass))
 			break;
 	}
@@ -479,12 +482,14 @@ int main(int argc, char* argv[])
 	/*
 	 * Mount filesystems
 	 */
+	if (!rescue) {
 #ifdef REMOUNT_ROOTFS
-	run("mount -n -o remount,rw /");
+		run("mount -n -o remount,rw /");
 #endif
 #ifdef SYSROOT
-	mount(SYSROOT, "/", NULL, MS_MOVE, NULL);
+		mount(SYSROOT, "/", NULL, MS_MOVE, NULL);
 #endif
+	}
 
 	/* Debian has this little script to copy generated rules while the system was read-only */
 	if (fexist("/lib/udev/udev-finish"))
@@ -493,15 +498,17 @@ int main(int argc, char* argv[])
 	/* Bootstrap conditions, needed for hooks */
 	cond_init();
 
-	_d("Root FS up, calling hooks ...");
+	if (!rescue) {
-	plugin_run_hooks(HOOK_ROOTFS_UP);
+		_d("Root FS up, calling hooks ...");
+		plugin_run_hooks(HOOK_ROOTFS_UP);
 
-	umask(0);
+		umask(0);
-	if (run_interactive("mount -na", "Mounting filesystems"))
+		if (run_interactive("mount -na", "Mounting filesystems"))
-		plugin_run_hooks(HOOK_MOUNT_ERROR);
+			plugin_run_hooks(HOOK_MOUNT_ERROR);
 
-	run("swapon -ea");
+		run("swapon -ea");
-	umask(0022);
+		umask(0022);
+	}
 
 	/* Base FS up, enable standard SysV init signals */
 	sig_setup(&loop);
@@ -512,8 +519,10 @@ int main(int argc, char* argv[])
 	 */
 	conf_monitor(&loop);
 
-	_d("Base FS up, calling hooks ...");
+	if (!rescue) {
-	plugin_run_hooks(HOOK_BASEFS_UP);
+		_d("Base FS up, calling hooks ...");
+		plugin_run_hooks(HOOK_BASEFS_UP);
+	}
 
 	/*
 	 * Initalize state machine and start all bootstrap tasks

src/finit.h

@@ -96,6 +96,7 @@ extern int    wdogpid;
 extern int    runlevel;
 extern int    cfglevel;
 extern int    prevlevel;
+extern int    rescue;
 extern char  *rcsd;
 extern char  *sdown;
 extern char  *network;

src/rescue.conf

@@ -0,0 +1,3 @@
+runlevel 1
+hostname rescue
+tty [12345] @console noclear nologin