switch_root: improve behavior on error; improve help text

*: make "can't execute '%s'" message uniform

archival/libunarchive/open_transformer.c

@@ -52,7 +52,7 @@ void FAST_FUNC open_transformer(int fd,
 			argv[2] = (char*)"-";
 			argv[3] = NULL;
 			BB_EXECVP(transform_prog, argv);
-			bb_perror_msg_and_die("can't exec %s", transform_prog);
+			bb_perror_msg_and_die("can't execute '%s'", transform_prog);
 		}
 #endif
 		/* notreached */

archival/tar.c

@@ -577,7 +577,7 @@ static void NOINLINE vfork_compressor(int tar_fd, int gzip)
 #endif
 	if (vfork_exec_errno) {
 		errno = vfork_exec_errno;
-		bb_perror_msg_and_die("cannot exec %s", zip_exec);
+		bb_perror_msg_and_die("can't execute '%s'", zip_exec);
 	}
 }
 #endif /* ENABLE_FEATURE_SEAMLESS_GZ || ENABLE_FEATURE_SEAMLESS_BZ2 */

coreutils/chroot.c

@@ -33,5 +33,5 @@ int chroot_main(int argc, char **argv)
 	}
 
 	BB_EXECVP(*argv, argv);
-	bb_perror_msg_and_die("cannot execute %s", *argv);
+	bb_perror_msg_and_die("can't execute '%s'", *argv);
 }

debianutils/run_parts.c

@@ -164,7 +164,7 @@ int run_parts_main(int argc UNUSED_PARAM, char **argv)
 			continue;
 		n = 1;
 		if (ret < 0)
-			bb_perror_msg("can't exec %s", name);
+			bb_perror_msg("can't execute '%s'", name);
 		else /* ret > 0 */
 			bb_error_msg("%s exited with code %d", name, ret);
 	}

include/usage.h

@@ -4125,12 +4125,13 @@
 	) \
 
 #define switch_root_trivial_usage \
-       "[-c /dev/console] NEW_ROOT NEW_INIT [ARGUMENTS_TO_INIT]"
+       "[-c /dev/console] NEW_ROOT NEW_INIT [ARG...]"
 #define switch_root_full_usage "\n\n" \
-       "Use from PID 1 under initramfs to free initramfs, chroot to NEW_ROOT,\n" \
-       "and exec NEW_INIT\n" \
+       "Free initramfs and switch to another root fs:\n" \
+       "chroot to NEW_ROOT, delete all in /, move NEW_ROOT to /,\n" \
+       "execute NEW_INIT. PID must be 1. NEW_ROOT must be a mountpoint.\n" \
      "\nOptions:" \
-     "\n	-c	Redirect console to device on new root" \
+     "\n	-c DEV	Reopen stdio to DEV after switch" \
 
 #define sync_trivial_usage \
        ""
@@ -4142,7 +4143,7 @@
 #define sysctl_full_usage "\n\n" \
        "Configure kernel parameters at runtime\n" \
      "\nOptions:" \
-     "\n	-n	Disable printing of key names" \
+     "\n	-n	Don't print key names" \
      "\n	-e	Don't warn about unknown keys" \
      "\n	-w	Change sysctl setting" \
      "\n	-p FILE	Load sysctl settings from FILE (default /etc/sysctl.conf)" \

loginutils/adduser.c

@@ -60,7 +60,7 @@ static void passwd_wrapper(const char *login)
 	static const char prog[] ALIGN1 = "passwd";
 
 	BB_EXECLP(prog, prog, login, NULL);
-	bb_error_msg_and_die("cannot execute %s, you must set password manually", prog);
+	bb_error_msg_and_die("can't execute %s, you must set password manually", prog);
 }
 
 #if ENABLE_FEATURE_ADDUSER_LONG_OPTIONS

selinux/runcon.c

@@ -129,10 +129,10 @@ int runcon_main(int argc UNUSED_PARAM, char **argv)
 				     context_str(con));
 
 	if (setexeccon(context_str(con)))
-		bb_error_msg_and_die("cannot set up security context '%s'",
+		bb_error_msg_and_die("can't set up security context '%s'",
 				     context_str(con));
 
 	execvp(argv[0], argv);
 
-	bb_perror_msg_and_die("cannot execute '%s'", argv[0]);
+	bb_perror_msg_and_die("can't execute '%s'", argv[0]);
 }

shell/cttyhack.c

@@ -73,5 +73,5 @@ int cttyhack_main(int argc UNUSED_PARAM, char **argv)
 	}
 
 	BB_EXECVP(argv[0], argv);
-	bb_perror_msg_and_die("cannot exec '%s'", argv[0]);
+	bb_perror_msg_and_die("can't execute '%s'", argv[0]);
 }

shell/hush.c

@@ -3048,7 +3048,7 @@ static void pseudo_exec_argv(nommu_save_t *nommu_save,
 	debug_printf_exec("execing '%s'\n", argv[0]);
 	sigprocmask(SIG_SETMASK, &G.inherited_set, NULL);
 	execvp(argv[0], argv);
-	bb_perror_msg("can't exec '%s'", argv[0]);
+	bb_perror_msg("can't execute '%s'", argv[0]);
 	_exit(EXIT_FAILURE);
 }
 

util-linux/switch_root.c

@@ -5,11 +5,10 @@
  *
  * Licensed under GPL version 2, see file LICENSE in this tarball for details.
  */
-
 #include "libbb.h"
 #include <sys/vfs.h>
 
-// Make up for header deficiencies.
+// Make up for header deficiencies
 #ifndef RAMFS_MAGIC
 #define RAMFS_MAGIC ((unsigned)0x858458f6)
 #endif
@@ -22,7 +21,7 @@
 #define MS_MOVE     8192
 #endif
 
-// Recursively delete contents of rootfs.
+// Recursively delete contents of rootfs
 static void delete_contents(const char *directory, dev_t rootdev)
 {
 	DIR *dir;
@@ -33,7 +32,7 @@ static void delete_contents(const char *directory, dev_t rootdev)
 	if (lstat(directory, &st) || st.st_dev != rootdev)
 		return;
 
-	// Recursively delete the contents of directories.
+	// Recursively delete the contents of directories
 	if (S_ISDIR(st.st_mode)) {
 		dir = opendir(directory);
 		if (dir) {
@@ -51,42 +50,47 @@ static void delete_contents(const char *directory, dev_t rootdev)
 			}
 			closedir(dir);
 
-			// Directory should now be empty.  Zap it.
+			// Directory should now be empty, zap it
 			rmdir(directory);
 		}
-
-	// It wasn't a directory.  Zap it.
-	} else unlink(directory);
+	} else {
+		// It wasn't a directory, zap it
+		unlink(directory);
+	}
 }
 
 int switch_root_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int switch_root_main(int argc UNUSED_PARAM, char **argv)
 {
 	char *newroot, *console = NULL;
-	struct stat st1, st2;
+	struct stat st;
 	struct statfs stfs;
 	dev_t rootdev;
 
 	// Parse args (-c console)
 	opt_complementary = "-2"; // minimum 2 params
-	getopt32(argv, "+c:", &console); // '+': stop parsing at first non-option
+	getopt32(argv, "+c:", &console); // '+': stop at first non-option
 	argv += optind;
-
-	// Change to new root directory and verify it's a different fs.
 	newroot = *argv++;
 
+	// Change to new root directory and verify it's a different fs
 	xchdir(newroot);
-	if (lstat(".", &st1) || lstat("/", &st2) || st1.st_dev == st2.st_dev) {
-		bb_error_msg_and_die("bad newroot %s", newroot);
+	xstat("/", &st);
+	rootdev = st.st_dev;
+	xstat(".", &st);
+	if (st.st_dev == rootdev || getpid() != 1) {
+		// Show usage, it says new root must be a mountpoint
+		// and we must be PID 1
+		bb_show_usage();
 	}
-	rootdev = st2.st_dev;
-
-	// Additional sanity checks: we're about to rm -rf /,  so be REALLY SURE
-	// we mean it.  (I could make this a CONFIG option, but I would get email
-	// from all the people who WILL eat their filesystems.)
-	if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs)
-	 || (((unsigned)stfs.f_type != RAMFS_MAGIC) && ((unsigned)stfs.f_type != TMPFS_MAGIC))
-	 || (getpid() != 1)
+
+	// Additional sanity checks: we're about to rm -rf /, so be REALLY SURE
+	// we mean it. I could make this a CONFIG option, but I would get email
+	// from all the people who WILL destroy their filesystems.
+	statfs("/", &stfs); // this never fails
+	if (lstat("/init", &st) != 0 || !S_ISREG(st.st_mode)
+	 || ((unsigned)stfs.f_type != RAMFS_MAGIC
+	     && (unsigned)stfs.f_type != TMPFS_MAGIC)
 	) {
 		bb_error_msg_and_die("not rootfs");
 	}
@@ -94,14 +98,16 @@ int switch_root_main(int argc UNUSED_PARAM, char **argv)
 	// Zap everything out of rootdev
 	delete_contents("/", rootdev);
 
-	// Overmount / with newdir and chroot into it.  The chdir is needed to
-	// recalculate "." and ".." links.
-	if (mount(".", "/", NULL, MS_MOVE, NULL))
+	// Overmount / with newdir and chroot into it
+	if (mount(".", "/", NULL, MS_MOVE, NULL)) {
+		// For example, fails when newroot is not a mountpoint
 		bb_perror_msg_and_die("error moving root");
+	}
+	// The chdir is needed to recalculate "." and ".." links
 	xchroot(".");
 	xchdir("/");
 
-	// If a new console specified, redirect stdin/stdout/stderr to that.
+	// If a new console specified, redirect stdin/stdout/stderr to it
 	if (console) {
 		close(0);
 		xopen(console, O_RDWR);
@@ -109,7 +115,7 @@ int switch_root_main(int argc UNUSED_PARAM, char **argv)
 		xdup2(0, 2);
 	}
 
-	// Exec real init.  (This is why we must be pid 1.)
+	// Exec real init
 	execv(argv[0], argv);
-	bb_perror_msg_and_die("bad init %s", argv[0]);
+	bb_perror_msg_and_die("can't execute '%s'", argv[0]);
 }