/bin/sh: can‘t access tty; job control turned off
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問題
最近在做嵌入式文件系統(tǒng)時使用了如下的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
::sysinit:/etc/init.d/rcS
::respawn:-/bin/sh
s3c2410_serial0::askfirst:-/bin/sh
::ctrlaltdel:/sbin/reboot
::shutdown:/bin/umount -a -r
結(jié)果出現(xiàn)了：/bin/sh: cant access tty; job control turned off
分析
BusyBox通過系統(tǒng)控制臺來做些工作, 如果我們的shell啟動在 /dev/console(5,1)上, tty_io.c 函數(shù)open中noctty就被設(shè)置成1,導(dǎo)致這個問題,具體原因還不知道。總之要啟動在一個真實的串口就沒有關(guān)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...
解決方法
可以通過BusyBox的init指定shell的設(shè)備, 注意, S3C2410上, 串口0是s3c2410_serial0。也就是說去掉::respawn:-/bin/sh就可以啦~~
串口名稱
串口名稱可以是s3c2410_serialx、ttySACx和ttySx等，但底層使用的是設(shè)備的主設(shè)備號和次設(shè)備號來定位具體設(shè)備的。所以不管是串口的名稱是什么
，只要主設(shè)備號和次設(shè)備號對了就可以。此外，通過mdev生成設(shè)備節(jié)點時，串口的名稱是s3c2410_serialx。
S3C2410的串口驅(qū)動文件drivers/serial/s3c2410.c中，有如下數(shù)據(jù)結(jié)構(gòu)：本文引用地址：http://www.ex-cimer.com/article/201611/319982.htm
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- staticstructuart_drivers3c24xx_uart_drv={
- .owner=THIS_MODULE,
- .dev_name="s3c2410_serial",
- .nr=3,
- .cons=S3C24XX_SERIAL_CONSOLE,
- .driver_name=S3C24XX_SERIAL_NAME,
- .major=S3C24XX_SERIAL_MAJOR,//主設(shè)備號為204
- .minor=S3C24XX_SERIAL_MINOR,//次設(shè)備號為64，這指第1個串口；第2個為65
- };
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