/bin/sh: can't access tty; job control turned off

问题

最近在做嵌入式文件系统时使用了如下的inittab文件：

#/etc/inittab
::sysinit:/etc/init.d/rcS
::respawn:-/bin/sh
s3c2410_serial0::askfirst:-/bin/sh
::ctrlaltdel:/sbin/reboot
::shutdown:/bin/umount -a -r

结果出现了：/bin/sh: can't access tty; job control turned off

分析

BusyBox通过系统控制台来做些工作, 如果我们的shell启动在 /dev/console(5,1)上, tty_io.c 函数open中noctty就被设置成1,导致这个问题,具体原因还不知道。总之要启动在一个真实的串口就没有关系。

Job control will be turned off since your shell can not obtain a controlling terminal. This typically happens when you run your shell on /dev/console. The kernel will not provide a controlling terminal on the /dev/console device. Your should run your shell on a normal tty such as tty1 or ttyS0 and everything will work perfectly. If you REALLY want your shell to run on /dev/console, then you can hack your kernel (if you are into that sortof thing) by changing drivers/char/tty_io.c to change the lines where it sets "noctty = 1;" to instead set it to "0". I recommend you instead run your shell on a real console...
解决方法

可以通过BusyBox的init指定shell的设备, 注意, S3C2410上, 串口0是s3c2410_serial0。也就是说去掉::respawn:-/bin/sh就可以啦~~

串口名称

串口名称可以是s3c2410_serialx、ttySACx和ttySx等，但底层使用的是设备的主设备号和次设备号来定位具体设备的。所以不管是串口的名称是什么
，只要主设备号和次设备号对了就可以。此外，通过mdev生成设备节点时，串口的名称是s3c2410_serialx。
S3C2410的串口驱动文件drivers/serial/s3c2410.c中，有如下数据结构：
static struct uart_driver s3c24xx_uart_drv = {.owner = THIS_MODULE,.dev_name = "s3c2410_serial",.nr = 3,.cons = S3C24XX_SERIAL_CONSOLE,.driver_name = S3C24XX_SERIAL_NAME,.major = S3C24XX_SERIAL_MAJOR,      // 主设备号为204.minor = S3C24XX_SERIAL_MINOR,      // 次设备号为64，这指第1个串口；第2个为65};
通过这个结构体就可以确定串口设备的主设备号和次设备号。