1.uboot的目标就是启动内核kernel；
2.kernel的目的就是启动应用程序，而第一个应用程序即是Init，构建根文件系统。
从uboot初始化配置后，引导内核的启动，启动函数为:start_kernel(void)
其他可以先不管，我们需要的是看看rest_init()函数;
代码如下：
1 asmlinkage void __init start_kernel(void) 2 { 3 char * command_line; 4 extern struct kernel_param __start___param[], __stop___param[]; 5 6 smp_setup_processor_id(); 7 8 /* 9 * Need to run as early as possible, to initialize the 10 * lockdep hash: 11 */ 12 lockdep_init(); 13 debug_objects_early_init(); 14 15 /* 16 * Set up the the initial canary ASAP: 17 */ 18 boot_init_stack_canary(); 19 20 cgroup_init_early(); 21 22 local_irq_disable(); 23 early_boot_irqs_off(); 24 early_init_irq_lock_class(); 25 26 /* 27 * Interrupts are still disabled. Do necessary setups, then 28 * enable them 29 */ 30 lock_kernel(); 31 tick_init(); 32 boot_cpu_init(); 33 page_address_init(); 34 printk(KERN_NOTICE "%s", linux_banner); 35 setup_arch(&command_line); 36 mm_init_owner(&init_mm, &init_task); 37 setup_command_line(command_line); 38 setup_nr_cpu_ids(); 39 setup_per_cpu_areas(); 40 smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */ 41 42 build_all_zonelists(NULL); 43 page_alloc_init(); 44 45 printk(KERN_NOTICE "Kernel command line: %s ", boot_command_line); 46 parse_early_param(); 47 parse_args("Booting kernel", static_command_line, __start___param, 48 __stop___param - __start___param, 49 &unknown_bootoption); 50 /* 51 * These use large bootmem allocations and must precede 52 * kmem_cache_init() 53 */ 54 pidhash_init(); 55 vfs_caches_init_early(); 56 sort_main_extable(); 57 trap_init(); 58 mm_init(); 59 /* 60 * Set up the scheduler prior starting any interrupts (such as the 61 * timer interrupt). Full topology setup happens at smp_init() 62 * time - but meanwhile we still have a functioning scheduler. 63 */ 64 sched_init(); 65 /* 66 * Disable preemption - early bootup scheduling is extremely 67 * fragile until we cpu_idle() for the first time. 68 */ 69 preempt_disable(); 70 if (!irqs_disabled()) { 71 printk(KERN_WARNING "start_kernel(): bug: interrupts were " 72 "enabled *very* early, fixing it "); 73 local_irq_disable(); 74 } 75 rcu_init(); 76 radix_tree_init(); 77 /* init some links before init_ISA_irqs() */ 78 early_irq_init(); 79 init_IRQ(); 80 prio_tree_init(); 81 init_timers(); 82 hrtimers_init(); 83 softirq_init(); 84 timekeeping_init(); 85 time_init(); 86 profile_init(); 87 if (!irqs_disabled()) 88 printk(KERN_CRIT "start_kernel(): bug: interrupts were " 89 "enabled early "); 90 early_boot_irqs_on(); 91 local_irq_enable(); 92 93 /* Interrupts are enabled now so all GFP allocations are safe. */ 94 gfp_allowed_mask = __GFP_BITS_MASK; 95 96 kmem_cache_init_late(); 97 98 /* 99 * HACK ALERT! This is early. We're enabling the console before 100 * we've done PCI setups etc, and console_init() must be aware of 101 * this. But we do want output early, in case something goes wrong. 102 */ 103 console_init(); 104 if (panic_later) 105 panic(panic_later, panic_param); 106 107 lockdep_info(); 108 109 /* 110 * Need to run this when irqs are enabled, because it wants 111 * to self-test [hard/soft]-irqs on/off lock inversion bugs 112 * too: 113 */ 114 locking_selftest(); 115 116 #ifdef CONFIG_BLK_DEV_INITRD 117 if (initrd_start && !initrd_below_start_ok && 118 page_to_pfn(virt_to_page((void *)initrd_start)) < min_low_pfn) { 119 printk(KERN_CRIT "initrd overwritten (0x%08lx < 0x%08lx) - " 120 "disabling it. ", 121 page_to_pfn(virt_to_page((void *)initrd_start)), 122 min_low_pfn); 123 initrd_start = 0; 124 } 125 #endif 126 page_cgroup_init(); 127 enable_debug_pagealloc(); 128 kmemtrace_init(); 129 kmemleak_init(); 130 debug_objects_mem_init(); 131 idr_init_cache(); 132 setup_per_cpu_pageset(); 133 numa_policy_init(); 134 if (late_time_init) 135 late_time_init(); 136 sched_clock_init(); 137 calibrate_delay(); 138 pidmap_init(); 139 anon_vma_init(); 140 #ifdef CONFIG_X86 141 if (efi_enabled) 142 efi_enter_virtual_mode(); 143 #endif 144 thread_info_cache_init(); 145 cred_init(); 146 fork_init(totalram_pages); 147 proc_caches_init(); 148 buffer_init(); 149 key_init(); 150 security_init(); 151 dbg_late_init(); 152 vfs_caches_init(totalram_pages); 153 signals_init(); 154 /* rootfs populating might need page-writeback */ 155 page_writeback_init(); 156 #ifdef CONFIG_PROC_FS 157 proc_root_init(); 158 #endif 159 cgroup_init(); 160 cpuset_init(); 161 taskstats_init_early(); 162 delayacct_init(); 163 164 check_bugs(); 165 166 acpi_early_init(); /* before LAPIC and SMP init */ 167 sfi_init_late(); 168 169 ftrace_init(); 170 171 /* Do the rest non-__init'ed, we're now alive */ 172 rest_init(); 173 }
rest_init()函数，如下：
static noinline void __init_refok rest_init(void)
__releases(kernel_lock)
{
int pid;
rcu_scheduler_starting();
/*
* We need to spawn init first so that it obtains pid 1, however
* the init task will end up wanting to create kthreads, which, if
* we schedule it before we create kthreadd, will OOPS.
*/
kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
numa_default_policy();
pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
rcu_read_lock();
kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
rcu_read_unlock();
complete(&kthreadd_done);
unlock_kernel();
/*
* The boot idle thread must execute schedule()
* at least once to get things moving:
*/
init_idle_bootup_task(current);
preempt_enable_no_resched();
schedule();
preempt_disable();
/* Call into cpu_idle with preempt disabled */
cpu_idle();
}
我们可以看到内核有一个内核的初始化线程：
kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
进入看看到底是实现什么东西：
static int __init kernel_init(void * unused)
{
/*
* Wait until kthreadd is all set-up.
*/
wait_for_completion(&kthreadd_done);
lock_kernel();
/*
* init can allocate pages on any node
*/
set_mems_allowed(node_states[N_HIGH_MEMORY]);
/*
* init can run on any cpu.
*/
set_cpus_allowed_ptr(current, cpu_all_mask);
/*
* Tell the world that we're going to be the grim
* reaper of innocent orphaned children.
*
* We don't want people to have to make incorrect
* assumptions about where in the task array this
* can be found.
*/
init_pid_ns.child_reaper = current;
cad_pid = task_pid(current);
smp_prepare_cpus(setup_max_cpus);
do_pre_smp_initcalls();
start_boot_trace();
smp_init();
sched_init_smp();
do_basic_setup();
/* Open the /dev/console on the rootfs, this should never fail */
if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
printk(KERN_WARNING "Warning: unable to open an initial console.
");
(void) sys_dup(0);
(void) sys_dup(0);
/*
* check if there is an early userspace init. If yes, let it do all
* the work
*/
if (!ramdisk_execute_command)
ramdisk_execute_command = "/init";
if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
ramdisk_execute_command = NULL;
prepare_namespace();
}
/*
* Ok, we have completed the initial bootup, and
* we're essentially up and running. Get rid of the
* initmem segments and start the user-mode stuff..
*/
init_post();
return 0;
}
if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0) printk(KERN_WARNING "Warning: unable to open an initial console. "); (void) sys_dup(0); (void) sys_dup(0);
上面代码实现的是控制台的输入，输出，还有error，好，现在，目前为止还没有看到真正的好东西，接着往下看
init_post();
static noinline int init_post(void) __releases(kernel_lock) { /* need to finish all async __init code before freeing the memory */ async_synchronize_full(); free_initmem(); unlock_kernel(); mark_rodata_ro(); system_state = SYSTEM_RUNNING; numa_default_policy(); current->signal->flags |= SIGNAL_UNKILLABLE; if (ramdisk_execute_command) { run_init_process(ramdisk_execute_command); printk(KERN_WARNING "Failed to execute %s ", ramdisk_execute_command); } /* * We try each of these until one succeeds. * * The Bourne shell can be used instead of init if we are * trying to recover a really broken machine. */ if (execute_command) { run_init_process(execute_command); printk(KERN_WARNING "Failed to execute %s. Attempting " "defaults... ", execute_command); } run_init_process("/sbin/init"); run_init_process("/etc/init"); run_init_process("/bin/init"); run_init_process("/bin/sh"); panic("No init found. Try passing init= option to kernel. " "See Linux Documentation/init.txt for guidance."); }
好东西终于出现了：
if (ramdisk_execute_command) { run_init_process(ramdisk_execute_command); printk(KERN_WARNING "Failed to execute %s ", ramdisk_execute_command); }
这个是干啥用的呢，搜索一下发现、
static int __init init_setup(char *str)
{
unsigned int i;
execute_command = str;
for (i = 1; i < MAX_INIT_ARGS; i++)
argv_init[i] = NULL;
return 1;
}
__setup("init=", init_setup);//设置命令行参数时候如：init=/linuxrc
查看一下：
# ls /linuxrc -l
lrwxrwxrwx 1 root root 11 Oct 25 2013 /linuxrc -> bin/busybox
那么linux就先启动/linuxrc
run_init_process("/sbin/init"); run_init_process("/etc/init"); run_init_process("/bin/init"); run_init_process("/bin/sh");
从函数名字来看run_init_process（“”）函数是用来初始化init进程的。在众多的书籍中，都介绍着，我们的linux系统最先启动的是init进程，我们可以直观的ps命令知道，init的pid = 1 因此我们有理由相信至此，我们找到好东西了。
首先 我们在linux的shell下
# ls /sbin/init -l
lrwxrwxrwx 1 root root 14 Oct 25 2013 /sbin/init -> ../bin/busybox
/sbin/init 指向/bin/busybox ；
至此我们发现所启动的程序都是指向busybox本身。因此我们需要分析busybox本身才能知道到底发生了什么.
解压busybox-1.16.1 建立工程。我们找到init.c的文件。当然里面也有cp.c ls.c等文件，linux是借助busybox来实现这些命令的，如果需要在应用程序里面实现某些类似功能可以参考busybox的源码。
我们先看init.c里面的main函数：
看看都做了什么东西：
1 int init_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; 2 int init_main(int argc UNUSED_PARAM, char **argv) 3 { 4 die_sleep = 30 * 24*60*60; /* if xmalloc would ever die... */ 5 6 if (argv[1] && strcmp(argv[1], "-q") == 0) { 7 return kill(1, SIGHUP); 8 } 9 10 if (!DEBUG_INIT) { 11 /* Expect to be invoked as init with PID=1 or be invoked as linuxrc */ 12 if (getpid() != 1 13 && (!ENABLE_FEATURE_INITRD || !strstr(applet_name, "linuxrc")) 14 ) { 15 bb_show_usage(); 16 } 17 /* Turn off rebooting via CTL-ALT-DEL - we get a 18 * SIGINT on CAD so we can shut things down gracefully... */ 19 reboot(RB_DISABLE_CAD); /* misnomer */ 20 } 21 22 /* Figure out where the default console should be */ 23 console_init(); 24 set_sane_term(); 25 xchdir("/"); 26 setsid(); 27 28 /* Make sure environs is set to something sane */ 29 putenv((char *) "HOME=/"); 30 putenv((char *) bb_PATH_root_path); 31 putenv((char *) "SHELL=/bin/sh"); 32 putenv((char *) "USER=root"); /* needed? why? */ 33 34 if (argv[1]) 35 xsetenv("RUNLEVEL", argv[1]); 36 37 #if !ENABLE_FEATURE_EXTRA_QUIET 38 /* Hello world */ 39 message(L_CONSOLE | L_LOG, "init started: %s", bb_banner); 40 #endif 41 42 /* Make sure there is enough memory to do something useful. */ 43 if (ENABLE_SWAPONOFF) { 44 struct sysinfo info; 45 46 if (sysinfo(&info) == 0 47 && (info.mem_unit ? info.mem_unit : 1) * (long long)info.totalram < 1024*1024 48 ) { 49 message(L_CONSOLE, "Low memory, forcing swapon"); 50 /* swapon -a requires /proc typically */ 51 new_init_action(SYSINIT, "mount -t proc proc /proc", ""); 52 /* Try to turn on swap */ 53 new_init_action(SYSINIT, "swapon -a", ""); 54 run_actions(SYSINIT); /* wait and removing */ 55 } 56 } 57 58 /* Check if we are supposed to be in single user mode */ 59 if (argv[1] 60 && (strcmp(argv[1], "single") == 0 || strcmp(argv[1], "-s") == 0 || LONE_CHAR(argv[1], '1')) 61 ) { 62 /* ??? shouldn't we set RUNLEVEL="b" here? */ 63 /* Start a shell on console */ 64 new_init_action(RESPAWN, bb_default_login_shell, ""); 65 } else { 66 /* Not in single user mode - see what inittab says */ 67 68 /* NOTE that if CONFIG_FEATURE_USE_INITTAB is NOT defined, 69 * then parse_inittab() simply adds in some default 70 * actions(i.e., INIT_SCRIPT and a pair 71 * of "askfirst" shells */ 72 parse_inittab(); 73 } 74 75 #if ENABLE_SELINUX 76 if (getenv("SELINUX_INIT") == NULL) { 77 int enforce = 0; 78 79 putenv((char*)"SELINUX_INIT=YES"); 80 if (selinux_init_load_policy(&enforce) == 0) { 81 BB_EXECVP(argv[0], argv); 82 } else if (enforce > 0) { 83 /* SELinux in enforcing mode but load_policy failed */ 84 message(L_CONSOLE, "can't load SELinux Policy. " 85 "Machine is in enforcing mode. Halting now."); 86 exit(EXIT_FAILURE); 87 } 88 } 89 #endif 90 91 /* Make the command line just say "init" - thats all, nothing else */ 92 strncpy(argv[0], "init", strlen(argv[0])); 93 /* Wipe argv[1]-argv[N] so they don't clutter the ps listing */ 94 while (*++argv) 95 memset(*argv, 0, strlen(*argv)); 96 97 /* Set up signal handlers */ 98 if (!DEBUG_INIT) { 99 struct sigaction sa; 100 101 bb_signals(0 102 + (1 << SIGUSR1) /* halt */ 103 + (1 << SIGTERM) /* reboot */ 104 + (1 << SIGUSR2) /* poweroff */ 105 , halt_reboot_pwoff); 106 signal(SIGQUIT, restart_handler); /* re-exec another init */ 107 108 /* Stop handler must allow only SIGCONT inside itself */ 109 memset(&sa, 0, sizeof(sa)); 110 sigfillset(&sa.sa_mask); 111 sigdelset(&sa.sa_mask, SIGCONT); 112 sa.sa_handler = stop_handler; 113 /* NB: sa_flags doesn't have SA_RESTART. 114 * It must be able to interrupt wait(). 115 */ 116 sigaction_set(SIGTSTP, &sa); /* pause */ 117 /* Does not work as intended, at least in 2.6.20. 118 * SIGSTOP is simply ignored by init: 119 */ 120 sigaction_set(SIGSTOP, &sa); /* pause */ 121 122 /* SIGINT (Ctrl-Alt-Del) must interrupt wait(), 123 * setting handler without SA_RESTART flag. 124 */ 125 bb_signals_recursive_norestart((1 << SIGINT), record_signo); 126 } 127 128 /* Set up "reread /etc/inittab" handler. 129 * Handler is set up without SA_RESTART, it will interrupt syscalls. 130 */ 131 if (!DEBUG_INIT && ENABLE_FEATURE_USE_INITTAB) 132 bb_signals_recursive_norestart((1 << SIGHUP), record_signo); 133 134 /* Now run everything that needs to be run */ 135 /* First run the sysinit command */ 136 run_actions(SYSINIT); 137 check_delayed_sigs(); 138 /* Next run anything that wants to block */ 139 run_actions(WAIT); 140 check_delayed_sigs(); 141 /* Next run anything to be run only once */ 142 run_actions(ONCE); 143 144 /* Now run the looping stuff for the rest of forever. 145 */ 146 while (1) { 147 int maybe_WNOHANG; 148 149 maybe_WNOHANG = check_delayed_sigs(); 150 151 /* (Re)run the respawn/askfirst stuff */ 152 run_actions(RESPAWN | ASKFIRST); 153 maybe_WNOHANG |= check_delayed_sigs(); 154 155 /* Don't consume all CPU time - sleep a bit */ 156 sleep(1); 157 maybe_WNOHANG |= check_delayed_sigs(); 158 159 /* Wait for any child process(es) to exit. 160 * 161 * If check_delayed_sigs above reported that a signal 162 * was caught, wait will be nonblocking. This ensures 163 * that if SIGHUP has reloaded inittab, respawn and askfirst 164 * actions will not be delayed until next child death. 165 */ 166 if (maybe_WNOHANG) 167 maybe_WNOHANG = WNOHANG; 168 while (1) { 169 pid_t wpid; 170 struct init_action *a; 171 172 /* If signals happen _in_ the wait, they interrupt it, 173 * bb_signals_recursive_norestart set them up that way 174 */ 175 wpid = waitpid(-1, NULL, maybe_WNOHANG); 176 if (wpid <= 0) 177 break; 178 179 a = mark_terminated(wpid); 180 if (a) { 181 message(L_LOG, "process '%s' (pid %d) exited. " 182 "Scheduling for restart.", 183 a->command, wpid); 184 } 185 /* See if anyone else is waiting to be reaped */ 186 maybe_WNOHANG = WNOHANG; 187 } 188 } /* while (1) */ 189 }
首先看一下
if (argv[1] 60 && (strcmp(argv[1], "single") == 0 || strcmp(argv[1], "-s") == 0 || LONE_CHAR(argv[1], '1')) 61 ) { 62 /* ??? shouldn't we set RUNLEVEL="b" here? */ 63 /* Start a shell on console */ 64 new_init_action(RESPAWN, bb_default_login_shell, ""); 65 } else { 66 /* Not in single user mode - see what inittab says */ 67 68 /* NOTE that if CONFIG_FEATURE_USE_INITTAB is NOT defined, 69 * then parse_inittab() simply adds in some default 70 * actions(i.e., INIT_SCRIPT and a pair 71 * of "askfirst" shells */ 72 parse_inittab(); 73 }
argv[1]参数是空的，实际上我们之前启动的内核init进程也是没有参数的，因此linux走的是另外的分支即是：
parse_inittab();
static void parse_inittab(void) { #if ENABLE_FEATURE_USE_INITTAB char *token[4]; parser_t *parser = config_open2("/etc/inittab", fopen_for_read); if (parser == NULL) #endif { /* No inittab file - set up some default behavior */ /* Reboot on Ctrl-Alt-Del */ new_init_action(CTRLALTDEL, "reboot", ""); /* Umount all filesystems on halt/reboot */ new_init_action(SHUTDOWN, "umount -a -r", ""); /* Swapoff on halt/reboot */ if (ENABLE_SWAPONOFF) new_init_action(SHUTDOWN, "swapoff -a", ""); /* Prepare to restart init when a QUIT is received */ new_init_action(RESTART, "init", ""); /* Askfirst shell on tty1-4 */ new_init_action(ASKFIRST, bb_default_login_shell, ""); //TODO: VC_1 instead of ""? "" is console -> ctty problems -> angry users new_init_action(ASKFIRST, bb_default_login_shell, VC_2); new_init_action(ASKFIRST, bb_default_login_shell, VC_3); new_init_action(ASKFIRST, bb_default_login_shell, VC_4); /* sysinit */ new_init_action(SYSINIT, INIT_SCRIPT, ""); return; } #if ENABLE_FEATURE_USE_INITTAB /* optional_tty:ignored_runlevel:action:command * Delims are not to be collapsed and need exactly 4 tokens */ while (config_read(parser, token, 4, 0, "#:", PARSE_NORMAL & ~(PARSE_TRIM | PARSE_COLLAPSE))) { /* order must correspond to SYSINIT..RESTART constants */ static const char actions[] ALIGN1 = "sysinit ""wait ""once ""respawn ""askfirst " "ctrlaltdel ""shutdown ""restart "; int action; char *tty = token[0]; if (!token[3]) /* less than 4 tokens */ goto bad_entry; action = index_in_strings(actions, token[2]); if (action < 0 || !token[3][0]) /* token[3]: command */ goto bad_entry; /* turn .*TTY -> /dev/TTY */ if (tty[0]) { if (strncmp(tty, "/dev/", 5) == 0) tty += 5; tty = concat_path_file("/dev/", tty); } new_init_action(1 << action, token[3], tty); if (tty[0]) free(tty); continue; bad_entry: message(L_LOG | L_CONSOLE, "Bad inittab entry at line %d", parser->lineno); } config_close(parser); #endif }
parser_t *parser = config_open2("/etc/inittab", fopen_for_read);
我们看名字可以得知此语句是去读取配置文件/etc/inittab。如果没有/etc/inittab文件（if (parser == NULL)），我们就给它配置一个默认的inittab文件
海思开发板下看一下：
# cat /etc/inittab # /etc/inittab init(8) configuration for BusyBox # # Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org> # # # Note, BusyBox init doesn't support runlevels. The runlevels field is # completely ignored by BusyBox init. If you want runlevels, use sysvinit. # # # Format for each entry: <id>:<runlevels>:<action>:<process> # # <id>: WARNING: This field has a non-traditional meaning for BusyBox init! # # The id field is used by BusyBox init to specify the controlling tty for # the specified process to run on. The contents of this field are # appended to "/dev/" and used as-is. There is no need for this field to # be unique, although if it isn't you may have strange results. If this # field is left blank, it is completely ignored. Also note that if # BusyBox detects that a serial console is in use, then all entries # containing non-empty id fields will _not_ be run. BusyBox init does # nothing with utmp. We don't need no stinkin' utmp. # # <runlevels>: The runlevels field is completely ignored. # # <action>: Valid actions include: sysinit, respawn, askfirst, wait, once, # restart, ctrlaltdel, and shutdown. # # Note: askfirst acts just like respawn, but before running the specified # process it displays the line "Please press Enter to activate this # console." and then waits for the user to press enter before starting # the specified process. # # Note: unrecognised actions (like initdefault) will cause init to emit # an error message, and then go along with its business. # # <process>: Specifies the process to be executed and it's command line. # # Note: BusyBox init works just fine without an inittab. If no inittab is # found, it has the following default behavior: # ::sysinit:/etc/init.d/rcS # ::askfirst:/bin/sh # ::ctrlaltdel:/sbin/reboot # ::shutdown:/sbin/swapoff -a # ::shutdown:/bin/umount -a -r # ::restart:/sbin/init # # if it detects that /dev/console is _not_ a serial console, it will # also run: # tty2::askfirst:/bin/sh # tty3::askfirst:/bin/sh # tty4::askfirst:/bin/sh # # Boot-time system configuration/initialization script. # This is run first except when booting in single-user mode. # ::sysinit:/etc/init.d/rcS # /bin/sh invocations on selected ttys # # Note below that we prefix the shell commands with a "-" to indicate to the # shell that it is supposed to be a login shell. Normally this is handled by # login, but since we are bypassing login in this case, BusyBox lets you do # this yourself... # # Start an "askfirst" shell on the console (whatever that may be) #::askfirst:-/bin/sh # Start an "askfirst" shell on /dev/tty2-4 # tty2::askfirst:-/bin/sh # tty3::askfirst:-/bin/sh # tty4::askfirst:-/bin/sh # /sbin/getty invocations for selected ttys # tty4::respawn:/sbin/getty 38400 tty5 # tty5::respawn:/sbin/getty 38400 tty6 # Example of how to put a getty on a serial line (for a terminal) ::respawn:/sbin/getty -L ttyS000 115200 vt100 -n root -I "Auto login as root ..." #::respawn:/sbin/getty -L ttyS1 9600 vt100 # # Example how to put a getty on a modem line. #::respawn:/sbin/getty 57600 ttyS2 # Stuff to do when restarting the init process ::restart:/sbin/init # Stuff to do before rebooting ::ctrlaltdel:/sbin/reboot ::shutdown:/bin/umount -a -r ::shutdown:/sbin/swapoff -a
前面两个冒号空的不用管，ctrlaltdel shutdown 是一下组合键或者操作的动作的信号发生后才运行的。
我们找到这句：new_init_action(1 << action, token[3], tty);
仔细读源码，我们可以知道它是将/etc/inittab配置文件的每一项执行完后就将其他从链表中删除。
我们在配置文件/etc/inittab发现一个脚本：
::sysinit:/etc/init.d/rcS
看看它想干嘛的：
#! /bin/sh /bin/mount -a echo " _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ / /__/ |_/ / __ / - _ ___ / / / / / / _ _ _ _/ / / \_/ \_ ______ ___________\___\__________________ " for initscript in /etc/init.d/S[0-9][0-9]* do if [ -x $initscript ] ; then echo "[RCS]: $initscript" $initscript fi done
我们发现一个很重要的一项：
/bin/mount -a 它的意思是将会执行/etc/fstab脚本。我们在海思平台上看一下：
# cat /etc/fstab proc /proc proc defaults 0 0 sysfs /sys sysfs defaults 0 0 tmpfs /dev tmpfs defaults 0 0
这里涉及一个udev机制，详细请查看文章mdev解析，这里意思是将linux虚拟的文件系统proc sysfs tmpfs 挂载到对应的目录这样，我们就不必要手动去创建了。
for initscript in /etc/init.d/S[0-9][0-9]* do if [ -x $initscript ] ; then echo "[RCS]: $initscript" $initscript fi done
上面的for循环是干嘛用的呢，我们可以大胆猜测下，应该是if（满足某种条件如具备可执行条件）就循环执行一个目录下的脚本。
我们去看看/etc/init.d/目录下都有哪些脚本：
# cd /etc/init.d/ # ls S00devs S01udev S80network S90modules rcS # cat S90modules #!/bin/sh telnetd& cd /kmod ./load cd -
我们挑一些来看看，如S90modules，发现它的作用就是启动/kmod/load脚本，我们再看看具体都做了哪些东西：
# cat /kmod/load rmmod ufsd rmmod ohci-hcd rmmod ehci-hcd rmmod png rmmod jpge rmmod jpeg rmmod hi_wdg rmmod hi_keyled rmmod hi_e2prom rmmod hi_cipher rmmod hi_ir rmmod hi_sci rmmod hifb rmmod hi_tuner rmmod hi_svdec.ko rmmod hi_mpi rmmod hi_ndpt rmmod hi_otp rmmod tde #rmmod hi_usbprotected rmmod hi_i2c rmmod hi_gpioi2c rmmod hi_gpio rmmod hi_dmac rmmod hi_common rmmod hi_mmz rmmod hi_c51 rmmod hi_media insmod hi_c51.ko insmod hi_mmz.ko insmod hi_common.ko insmod hi_dmac.ko insmod hi_gpio.ko insmod hi_gpioi2c.ko gpioidclock=11 clockbit=3 gpioiddata=12 databit=5 i2cmode=2 insmod hi_i2c.ko #insmod hi_usbprotected.ko Usb0PwrEn=63 Usb0Ovrcur=65 Usb0IntType=1 insmod tde.ko insmod hi_otp.ko insmod hi_ndpt.ko insmod hi_mpi.ko insmod hi_svdec.ko insmod hi_tuner.ko insmod hifb.ko video="hifb:vram0_size:2430, vram2_size:7200" insmod hi_sci.ko insmod hi_ir.ko insmod hi_cipher.ko insmod hi_e2prom.ko insmod hi_keyled.ko insmod hi_wdg.ko insmod jpeg.ko insmod jpge.ko insmod png.ko insmod /kmod/usb/ehci-hcd.ko insmod /kmod/usb/ohci-hcd.ko echo 3 > /proc/sys/vm/dirty_ratio insmod ufsd.ko mount -t squashfs /dev/romblock11 /home mount -t yaffs2 /dev/mtdblock12 /reserved mount -t yaffs2 /dev/mtdblock13 /mnt mount -t tmpfs nodev /tmp echo 1 > /proc/sys/vm/overcommit_memory echo 8192 > /proc/sys/vm/min_free_kbytes
我们不难知道，load脚本主要是执行一些驱动模块的卸载，加载，还有将/dev下的一些分区用正确的格式挂载到对应的目录下。
至此，我们的分析基本完毕，另外还有app的启动也是用脚本，在进入linux时候启动起来的。
# pwd /etc # cat profile # /etc/profile: system-wide .profile file for the Bourne shells # # set_path_before() { [ -d $1 ] && PATH="$1:$PATH" } PATH="/usr/bin:/usr/sbin:/bin:/sbin" set_path_before /usr/local/sbin set_path_before /usr/local/bin LD_LIBRARY_PATH="/usr/local/lib:/usr/lib" export PATH export LD_LIBRARY_PATH # ANSI COLORS " NORMAL="" RED="" GREEN="" YELLOW="" BLUE="" MAGENTA="" CYAN="" WHITE="" umask 022 if [ -e /tmp/run_flag ]; then echo "app is running already! " exit 0 else touch /tmp/run_flag fi #ifconfig eth1 192.168.5.177 #route add DEFAULT 192.168.5.177 #ifconfig lo 127.0.0.1 #/usr/sbin/udhcpd -S /etc/udhcpd.conf #echo "1" >/proc/sys/net/ipv4/ip_forward #cd /etc #./iptables.sh himm 0x600d1310 0x5F1 ifconfig eth0 up ifconfig eth1 up echo "${GREEN}Welcome to HiLinux.${NORMAL}" cd /home while true do ./appmain killall -9 udhcpc usleep 300000 ./appmain 100 done
/etc/profile 文件是登陆linux时候就运行的，app此时启动了。
# cat /etc/fstab proc /proc proc defaults 0 0sysfs /sys sysfs defaults 0 0tmpfs /dev tmpfs defaults 0 0