init/main.c

   1 /*
   2  *  linux/init/main.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  *
   6  *  GK 2/5/95  -  Changed to support mounting root fs via NFS
   7  *  Added initrd & change_root: Werner Almesberger & Hans Lermen, Feb '96
   8  *  Moan early if gcc is old, avoiding bogus kernels - Paul Gortmaker, May '96
   9  *  Simplified starting of init:  Michael A. Griffith <grif@acm.org>
  10  */
  11
  12 #define __KERNEL_SYSCALLS__
  13
  14 #include <linux/types.h>
  15 #include <linux/module.h>
  16 #include <linux/proc_fs.h>
  17 #include <linux/kernel.h>
  18 #include <linux/syscalls.h>
  19 #include <linux/string.h>
  20 #include <linux/ctype.h>
  21 #include <linux/delay.h>
  22 #include <linux/utsname.h>
  23 #include <linux/ioport.h>
  24 #include <linux/init.h>
  25 #include <linux/smp_lock.h>
  26 #include <linux/initrd.h>
  27 #include <linux/hdreg.h>
  28 #include <linux/bootmem.h>
  29 #include <linux/tty.h>
  30 #include <linux/gfp.h>
  31 #include <linux/percpu.h>
  32 #include <linux/kmod.h>
  33 #include <linux/kernel_stat.h>
  34 #include <linux/security.h>
  35 #include <linux/workqueue.h>
  36 #include <linux/profile.h>
  37 #include <linux/rcupdate.h>
  38 #include <linux/moduleparam.h>
  39 #include <linux/kallsyms.h>
  40 #include <linux/writeback.h>
  41 #include <linux/cpu.h>
  42 #include <linux/cpuset.h>
  43 #include <linux/efi.h>
  44 #include <linux/delayacct.h>
  45 #include <linux/unistd.h>
  46 #include <linux/rmap.h>
  47 #include <linux/mempolicy.h>
  48 #include <linux/key.h>
  49 #include <linux/unwind.h>
  50 #include <linux/buffer_head.h>
  51 #include <linux/debug_locks.h>
  52 #include <linux/lockdep.h>
  53
  54 #include <asm/io.h>
  55 #include <asm/bugs.h>
  56 #include <asm/setup.h>
  57 #include <asm/sections.h>
  58 #include <asm/cacheflush.h>
  59
  60 #ifdef CONFIG_X86_LOCAL_APIC
  61 #include <asm/smp.h>
  62 #endif
  63
  64 /*
  65  * This is one of the first .c files built. Error out early if we have compiler
  66  * trouble.
  67  *
  68  * Versions of gcc older than that listed below may actually compile and link
  69  * okay, but the end product can have subtle run time bugs.  To avoid associated
  70  * bogus bug reports, we flatly refuse to compile with a gcc that is known to be
  71  * too old from the very beginning.
  72  */
  73 #if (__GNUC__ < 3) || (__GNUC__ == 3 && __GNUC_MINOR__ < 2)
  74 #error Sorry, your GCC is too old. It builds incorrect kernels.
  75 #endif
  76
  77 static int init(void *);
  78
  79 extern void init_IRQ(void);
  80 extern void fork_init(unsigned long);
  81 extern void mca_init(void);
  82 extern void sbus_init(void);
  83 extern void sysctl_init(void);
  84 extern void signals_init(void);
  85 extern void pidhash_init(void);
  86 extern void pidmap_init(void);
  87 extern void prio_tree_init(void);
  88 extern void radix_tree_init(void);
  89 extern void free_initmem(void);
  90 extern void populate_rootfs(void);
  91 extern void driver_init(void);
  92 extern void prepare_namespace(void);
  93 #ifdef  CONFIG_ACPI
  94 extern void acpi_early_init(void);
  95 #else
  96 static inline void acpi_early_init(void) { }
  97 #endif
  98 #ifndef CONFIG_DEBUG_RODATA
  99 static inline void mark_rodata_ro(void) { }
 100 #endif
 101
 102 #ifdef CONFIG_TC
 103 extern void tc_init(void);
 104 #endif
 105
 106 enum system_states system_state;
 107 EXPORT_SYMBOL(system_state);
 108
 109 /*
 110  * Boot command-line arguments
 111  */
 112 #define MAX_INIT_ARGS CONFIG_INIT_ENV_ARG_LIMIT
 113 #define MAX_INIT_ENVS CONFIG_INIT_ENV_ARG_LIMIT
 114
 115 extern void time_init(void);
 116 /* Default late time init is NULL. archs can override this later. */
 117 void (*late_time_init)(void);
 118 extern void softirq_init(void);
 119
 120 /* Untouched command line (eg. for /proc) saved by arch-specific code. */
 121 char saved_command_line[COMMAND_LINE_SIZE];
 122
 123 static char *execute_command;
 124 static char *ramdisk_execute_command;
 125
 126 /* Setup configured maximum number of CPUs to activate */
 127 static unsigned int max_cpus = NR_CPUS;
 128
 129 /*
 130  * Setup routine for controlling SMP activation
 131  *
 132  * Command-line option of "nosmp" or "maxcpus=0" will disable SMP
 133  * activation entirely (the MPS table probe still happens, though).
 134  *
 135  * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer
 136  * greater than 0, limits the maximum number of CPUs activated in
 137  * SMP mode to <NUM>.
 138  */
 139 static int __init nosmp(char *str)
 140 {
 141         max_cpus = 0;
 142         return 1;
 143 }
 144
 145 __setup("nosmp", nosmp);
 146
 147 static int __init maxcpus(char *str)
 148 {
 149         get_option(&str, &max_cpus);
 150         return 1;
 151 }
 152
 153 __setup("maxcpus=", maxcpus);
 154
 155 static char * argv_init[MAX_INIT_ARGS+2] = { "init", NULL, };
 156 char * envp_init[MAX_INIT_ENVS+2] = { "HOME=/", "TERM=linux", NULL, };
 157 static const char *panic_later, *panic_param;
 158
 159 extern struct obs_kernel_param __setup_start[], __setup_end[];
 160
 161 static int __init obsolete_checksetup(char *line)
 162 {
 163         struct obs_kernel_param *p;
 164
 165         p = __setup_start;
 166         do {
 167                 int n = strlen(p->str);
 168                 if (!strncmp(line, p->str, n)) {
 169                         if (p->early) {
 170                                 /* Already done in parse_early_param?  (Needs
 171                                  * exact match on param part) */
 172                                 if (line[n] == '\0' || line[n] == '=')
 173                                         return 1;
 174                         } else if (!p->setup_func) {
 175                                 printk(KERN_WARNING "Parameter %s is obsolete,"
 176                                        " ignored\n", p->str);
 177                                 return 1;
 178                         } else if (p->setup_func(line + n))
 179                                 return 1;
 180                 }
 181                 p++;
 182         } while (p < __setup_end);
 183         return 0;
 184 }
 185
 186 /*
 187  * This should be approx 2 Bo*oMips to start (note initial shift), and will
 188  * still work even if initially too large, it will just take slightly longer
 189  */
 190 unsigned long loops_per_jiffy = (1<<12);
 191
 192 EXPORT_SYMBOL(loops_per_jiffy);
 193
 194 static int __init debug_kernel(char *str)
 195 {
 196         if (*str)
 197                 return 0;
 198         console_loglevel = 10;
 199         return 1;
 200 }
 201
 202 static int __init quiet_kernel(char *str)
 203 {
 204         if (*str)
 205                 return 0;
 206         console_loglevel = 4;
 207         return 1;
 208 }
 209
 210 __setup("debug", debug_kernel);
 211 __setup("quiet", quiet_kernel);
 212
 213 static int __init loglevel(char *str)
 214 {
 215         get_option(&str, &console_loglevel);
 216         return 1;
 217 }
 218
 219 __setup("loglevel=", loglevel);
 220
 221 /*
 222  * Unknown boot options get handed to init, unless they look like
 223  * failed parameters
 224  */
 225 static int __init unknown_bootoption(char *param, char *val)
 226 {
 227         /* Change NUL term back to "=", to make "param" the whole string. */
 228         if (val) {
 229                 /* param=val or param="val"? */
 230                 if (val == param+strlen(param)+1)
 231                         val[-1] = '=';
 232                 else if (val == param+strlen(param)+2) {
 233                         val[-2] = '=';
 234                         memmove(val-1, val, strlen(val)+1);
 235                         val--;
 236                 } else
 237                         BUG();
 238         }
 239
 240         /* Handle obsolete-style parameters */
 241         if (obsolete_checksetup(param))
 242                 return 0;
 243
 244         /*
 245          * Preemptive maintenance for "why didn't my mispelled command
 246          * line work?"
 247          */
 248         if (strchr(param, '.') && (!val || strchr(param, '.') < val)) {
 249                 printk(KERN_ERR "Unknown boot option `%s': ignoring\n", param);
 250                 return 0;
 251         }
 252
 253         if (panic_later)
 254                 return 0;
 255
 256         if (val) {
 257                 /* Environment option */
 258                 unsigned int i;
 259                 for (i = 0; envp_init[i]; i++) {
 260                         if (i == MAX_INIT_ENVS) {
 261                                 panic_later = "Too many boot env vars at `%s'";
 262                                 panic_param = param;
 263                         }
 264                         if (!strncmp(param, envp_init[i], val - param))
 265                                 break;
 266                 }
 267                 envp_init[i] = param;
 268         } else {
 269                 /* Command line option */
 270                 unsigned int i;
 271                 for (i = 0; argv_init[i]; i++) {
 272                         if (i == MAX_INIT_ARGS) {
 273                                 panic_later = "Too many boot init vars at `%s'";
 274                                 panic_param = param;
 275                         }
 276                 }
 277                 argv_init[i] = param;
 278         }
 279         return 0;
 280 }
 281
 282 static int __init init_setup(char *str)
 283 {
 284         unsigned int i;
 285
 286         execute_command = str;
 287         /*
 288          * In case LILO is going to boot us with default command line,
 289          * it prepends "auto" before the whole cmdline which makes
 290          * the shell think it should execute a script with such name.
 291          * So we ignore all arguments entered _before_ init=... [MJ]
 292          */
 293         for (i = 1; i < MAX_INIT_ARGS; i++)
 294                 argv_init[i] = NULL;
 295         return 1;
 296 }
 297 __setup("init=", init_setup);
 298
 299 static int __init rdinit_setup(char *str)
 300 {
 301         unsigned int i;
 302
 303         ramdisk_execute_command = str;
 304         /* See "auto" comment in init_setup */
 305         for (i = 1; i < MAX_INIT_ARGS; i++)
 306                 argv_init[i] = NULL;
 307         return 1;
 308 }
 309 __setup("rdinit=", rdinit_setup);
 310
 311 #ifndef CONFIG_SMP
 312
 313 #ifdef CONFIG_X86_LOCAL_APIC
 314 static void __init smp_init(void)
 315 {
 316         APIC_init_uniprocessor();
 317 }
 318 #else
 319 #define smp_init()      do { } while (0)
 320 #endif
 321
 322 static inline void setup_per_cpu_areas(void) { }
 323 static inline void smp_prepare_cpus(unsigned int maxcpus) { }
 324
 325 #else
 326
 327 #ifdef __GENERIC_PER_CPU
 328 unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
 329
 330 EXPORT_SYMBOL(__per_cpu_offset);
 331
 332 static void __init setup_per_cpu_areas(void)
 333 {
 334         unsigned long size, i;
 335         char *ptr;
 336         unsigned long nr_possible_cpus = num_possible_cpus();
 337
 338         /* Copy section for each CPU (we discard the original) */
 339         size = ALIGN(__per_cpu_end - __per_cpu_start, SMP_CACHE_BYTES);
 340 #ifdef CONFIG_MODULES
 341         if (size < PERCPU_ENOUGH_ROOM)
 342                 size = PERCPU_ENOUGH_ROOM;
 343 #endif
 344         ptr = alloc_bootmem(size * nr_possible_cpus);
 345
 346         for_each_possible_cpu(i) {
 347                 __per_cpu_offset[i] = ptr - __per_cpu_start;
 348                 memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start);
 349                 ptr += size;
 350         }
 351 }
 352 #endif /* !__GENERIC_PER_CPU */
 353
 354 /* Called by boot processor to activate the rest. */
 355 static void __init smp_init(void)
 356 {
 357         unsigned int i;
 358
 359         /* FIXME: This should be done in userspace --RR */
 360         for_each_present_cpu(i) {
 361                 if (num_online_cpus() >= max_cpus)
 362                         break;
 363                 if (!cpu_online(i))
 364                         cpu_up(i);
 365         }
 366
 367         /* Any cleanup work */
 368         printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus());
 369         smp_cpus_done(max_cpus);
 370 #if 0
 371         /* Get other processors into their bootup holding patterns. */
 372
 373         smp_commence();
 374 #endif
 375 }
 376
 377 #endif
 378
 379 /*
 380  * We need to finalize in a non-__init function or else race conditions
 381  * between the root thread and the init thread may cause start_kernel to
 382  * be reaped by free_initmem before the root thread has proceeded to
 383  * cpu_idle.
 384  *
 385  * gcc-3.4 accidentally inlines this function, so use noinline.
 386  */
 387
 388 static void noinline rest_init(void)
 389         __releases(kernel_lock)
 390 {
 391         kernel_thread(init, NULL, CLONE_FS | CLONE_SIGHAND);
 392         numa_default_policy();
 393         unlock_kernel();
 394
 395         /*
 396          * The boot idle thread must execute schedule()
 397          * at least one to get things moving:
 398          */
 399         preempt_enable_no_resched();
 400         schedule();
 401         preempt_disable();
 402
 403         /* Call into cpu_idle with preempt disabled */
 404         cpu_idle();
 405 }
 406
 407 /* Check for early params. */
 408 static int __init do_early_param(char *param, char *val)
 409 {
 410         struct obs_kernel_param *p;
 411
 412         for (p = __setup_start; p < __setup_end; p++) {
 413                 if (p->early && strcmp(param, p->str) == 0) {
 414                         if (p->setup_func(val) != 0)
 415                                 printk(KERN_WARNING
 416                                        "Malformed early option '%s'\n", param);
 417                 }
 418         }
 419         /* We accept everything at this stage. */
 420         return 0;
 421 }
 422
 423 /* Arch code calls this early on, or if not, just before other parsing. */
 424 void __init parse_early_param(void)
 425 {
 426         static __initdata int done = 0;
 427         static __initdata char tmp_cmdline[COMMAND_LINE_SIZE];
 428
 429         if (done)
 430                 return;
 431
 432         /* All fall through to do_early_param. */
 433         strlcpy(tmp_cmdline, saved_command_line, COMMAND_LINE_SIZE);
 434         parse_args("early options", tmp_cmdline, NULL, 0, do_early_param);
 435         done = 1;
 436 }
 437
 438 /*
 439  *      Activate the first processor.
 440  */
 441
 442 static void __init boot_cpu_init(void)
 443 {
 444         int cpu = smp_processor_id();
 445         /* Mark the boot cpu "present", "online" etc for SMP and UP case */
 446         cpu_set(cpu, cpu_online_map);
 447         cpu_set(cpu, cpu_present_map);
 448         cpu_set(cpu, cpu_possible_map);
 449 }
 450
 451 void __init __attribute__((weak)) smp_setup_processor_id(void)
 452 {
 453 }
 454
 455 asmlinkage void __init start_kernel(void)
 456 {
 457         char * command_line;
 458         extern struct kernel_param __start___param[], __stop___param[];
 459
 460         smp_setup_processor_id();
 461
 462         /*
 463          * Need to run as early as possible, to initialize the
 464          * lockdep hash:
 465          */
 466         lockdep_init();
 467
 468         local_irq_disable();
 469         early_boot_irqs_off();
 470         early_init_irq_lock_class();
 471
 472 /*
 473  * Interrupts are still disabled. Do necessary setups, then
 474  * enable them
 475  */
 476         lock_kernel();
 477         boot_cpu_init();
 478         page_address_init();
 479         printk(KERN_NOTICE);
 480         printk(linux_banner);
 481         setup_arch(&command_line);
 482         setup_per_cpu_areas();
 483         smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
 484
 485         /*
 486          * Set up the scheduler prior starting any interrupts (such as the
 487          * timer interrupt). Full topology setup happens at smp_init()
 488          * time - but meanwhile we still have a functioning scheduler.
 489          */
 490         sched_init();
 491         /*
 492          * Disable preemption - early bootup scheduling is extremely
 493          * fragile until we cpu_idle() for the first time.
 494          */
 495         preempt_disable();
 496         build_all_zonelists();
 497         page_alloc_init();
 498         printk(KERN_NOTICE "Kernel command line: %s\n", saved_command_line);
 499         parse_early_param();
 500         parse_args("Booting kernel", command_line, __start___param,
 501                    __stop___param - __start___param,
 502                    &unknown_bootoption);
 503         sort_main_extable();
 504         unwind_init();
 505         trap_init();
 506         rcu_init();
 507         init_IRQ();
 508         pidhash_init();
 509         init_timers();
 510         hrtimers_init();
 511         softirq_init();
 512         timekeeping_init();
 513         time_init();
 514         profile_init();
 515         if (!irqs_disabled())
 516                 printk("start_kernel(): bug: interrupts were enabled early\n");
 517         early_boot_irqs_on();
 518         local_irq_enable();
 519
 520         /*
 521          * HACK ALERT! This is early. We're enabling the console before
 522          * we've done PCI setups etc, and console_init() must be aware of
 523          * this. But we do want output early, in case something goes wrong.
 524          */
 525         console_init();
 526         if (panic_later)
 527                 panic(panic_later, panic_param);
 528
 529         lockdep_info();
 530
 531         /*
 532          * Need to run this when irqs are enabled, because it wants
 533          * to self-test [hard/soft]-irqs on/off lock inversion bugs
 534          * too:
 535          */
 536         locking_selftest();
 537
 538 #ifdef CONFIG_BLK_DEV_INITRD
 539         if (initrd_start && !initrd_below_start_ok &&
 540                         initrd_start < min_low_pfn << PAGE_SHIFT) {
 541                 printk(KERN_CRIT "initrd overwritten (0x%08lx < 0x%08lx) - "
 542                     "disabling it.\n",initrd_start,min_low_pfn << PAGE_SHIFT);
 543                 initrd_start = 0;
 544         }
 545 #endif
 546         vfs_caches_init_early();
 547         cpuset_init_early();
 548         mem_init();
 549         kmem_cache_init();
 550         setup_per_cpu_pageset();
 551         numa_policy_init();
 552         if (late_time_init)
 553                 late_time_init();
 554         calibrate_delay();
 555         pidmap_init();
 556         pgtable_cache_init();
 557         prio_tree_init();
 558         anon_vma_init();
 559 #ifdef CONFIG_X86
 560         if (efi_enabled)
 561                 efi_enter_virtual_mode();
 562 #endif
 563         fork_init(num_physpages);
 564         proc_caches_init();
 565         buffer_init();
 566         unnamed_dev_init();
 567         key_init();
 568         security_init();
 569         vfs_caches_init(num_physpages);
 570         radix_tree_init();
 571         signals_init();
 572         /* rootfs populating might need page-writeback */
 573         page_writeback_init();
 574 #ifdef CONFIG_PROC_FS
 575         proc_root_init();
 576 #endif
 577         cpuset_init();
 578         delayacct_init();
 579
 580         check_bugs();
 581
 582         acpi_early_init(); /* before LAPIC and SMP init */
 583
 584         /* Do the rest non-__init'ed, we're now alive */
 585         rest_init();
 586 }
 587
 588 static int __initdata initcall_debug;
 589
 590 static int __init initcall_debug_setup(char *str)
 591 {
 592         initcall_debug = 1;
 593         return 1;
 594 }
 595 __setup("initcall_debug", initcall_debug_setup);
 596
 597 struct task_struct *child_reaper = &init_task;
 598
 599 extern initcall_t __initcall_start[], __initcall_end[];
 600
 601 static void __init do_initcalls(void)
 602 {
 603         initcall_t *call;
 604         int count = preempt_count();
 605
 606         for (call = __initcall_start; call < __initcall_end; call++) {
 607                 char *msg = NULL;
 608                 char msgbuf[40];
 609                 int result;
 610
 611                 if (initcall_debug) {
 612                         printk("Calling initcall 0x%p", *call);
 613                         print_fn_descriptor_symbol(": %s()",
 614                                         (unsigned long) *call);
 615                         printk("\n");
 616                 }
 617
 618                 result = (*call)();
 619
 620                 if (result && result != -ENODEV && initcall_debug) {
 621                         sprintf(msgbuf, "error code %d", result);
 622                         msg = msgbuf;
 623                 }
 624                 if (preempt_count() != count) {
 625                         msg = "preemption imbalance";
 626                         preempt_count() = count;
 627                 }
 628                 if (irqs_disabled()) {
 629                         msg = "disabled interrupts";
 630                         local_irq_enable();
 631                 }
 632                 if (msg) {
 633                         printk(KERN_WARNING "initcall at 0x%p", *call);
 634                         print_fn_descriptor_symbol(": %s()",
 635                                         (unsigned long) *call);
 636                         printk(": returned with %s\n", msg);
 637                 }
 638         }
 639
 640         /* Make sure there is no pending stuff from the initcall sequence */
 641         flush_scheduled_work();
 642 }
 643
 644 /*
 645  * Ok, the machine is now initialized. None of the devices
 646  * have been touched yet, but the CPU subsystem is up and
 647  * running, and memory and process management works.
 648  *
 649  * Now we can finally start doing some real work..
 650  */
 651 static void __init do_basic_setup(void)
 652 {
 653         /* drivers will send hotplug events */
 654         init_workqueues();
 655         usermodehelper_init();
 656         driver_init();
 657
 658 #ifdef CONFIG_SYSCTL
 659         sysctl_init();
 660 #endif
 661
 662         do_initcalls();
 663 }
 664
 665 static void do_pre_smp_initcalls(void)
 666 {
 667         extern int spawn_ksoftirqd(void);
 668 #ifdef CONFIG_SMP
 669         extern int migration_init(void);
 670
 671         migration_init();
 672 #endif
 673         spawn_ksoftirqd();
 674         spawn_softlockup_task();
 675 }
 676
 677 static void run_init_process(char *init_filename)
 678 {
 679         argv_init[0] = init_filename;
 680         execve(init_filename, argv_init, envp_init);
 681 }
 682
 683 static int init(void * unused)
 684 {
 685         lock_kernel();
 686         /*
 687          * init can run on any cpu.
 688          */
 689         set_cpus_allowed(current, CPU_MASK_ALL);
 690         /*
 691          * Tell the world that we're going to be the grim
 692          * reaper of innocent orphaned children.
 693          *
 694          * We don't want people to have to make incorrect
 695          * assumptions about where in the task array this
 696          * can be found.
 697          */
 698         child_reaper = current;
 699
 700         smp_prepare_cpus(max_cpus);
 701
 702         do_pre_smp_initcalls();
 703
 704         smp_init();
 705         sched_init_smp();
 706
 707         cpuset_init_smp();
 708
 709         /*
 710          * Do this before initcalls, because some drivers want to access
 711          * firmware files.
 712          */
 713         populate_rootfs();
 714
 715         do_basic_setup();
 716
 717         /*
 718          * check if there is an early userspace init.  If yes, let it do all
 719          * the work
 720          */
 721
 722         if (!ramdisk_execute_command)
 723                 ramdisk_execute_command = "/init";
 724
 725         if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
 726                 ramdisk_execute_command = NULL;
 727                 prepare_namespace();
 728         }
 729
 730         /*
 731          * Ok, we have completed the initial bootup, and
 732          * we're essentially up and running. Get rid of the
 733          * initmem segments and start the user-mode stuff..
 734          */
 735         free_initmem();
 736         unlock_kernel();
 737         mark_rodata_ro();
 738         system_state = SYSTEM_RUNNING;
 739         numa_default_policy();
 740
 741         if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
 742                 printk(KERN_WARNING "Warning: unable to open an initial console.\n");
 743
 744         (void) sys_dup(0);
 745         (void) sys_dup(0);
 746
 747         if (ramdisk_execute_command) {
 748                 run_init_process(ramdisk_execute_command);
 749                 printk(KERN_WARNING "Failed to execute %s\n",
 750                                 ramdisk_execute_command);
 751         }
 752
 753         /*
 754          * We try each of these until one succeeds.
 755          *
 756          * The Bourne shell can be used instead of init if we are
 757          * trying to recover a really broken machine.
 758          */
 759         if (execute_command) {
 760                 run_init_process(execute_command);
 761                 printk(KERN_WARNING "Failed to execute %s.  Attempting "
 762                                         "defaults...\n", execute_command);
 763         }
 764         run_init_process("/sbin/init");
 765         run_init_process("/etc/init");
 766         run_init_process("/bin/init");
 767         run_init_process("/bin/sh");
 768
 769         panic("No init found.  Try passing init= option to kernel.");
 770 }