Changes between Initial Version and Version 1 of silenceconsole


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Timestamp:
10/22/2017 05:28:45 AM (2 years ago)
Author:
trac
Comment:

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  • silenceconsole

    v1 v1  
     1[[PageOutline]]
     2
     3= Disabling Serial Console =
     4For varying privacy and security reasons, some people like to completely silence the serial console output. This needs to be done in the following places:
     5 * [#bootloader Bootloader] (serial console)
     6 * [#kernel Linux Kernel] (serial console)
     7 * [#linuxos Linux OS] (console login)
     8
     9''' Please NOTE: There will be no way to access the board besides over the network after making these changes.'''
     10
     11''' Please make changes at your own risk'''
     12
     13Recovery would be through re-programming the board via the Gateworks JTAG Programmer.
     14
     15[=#bootloader]
     16== Disable U-Boot bootloader serial console ==
     17In order to disable serial console for the U-Boot bootloader you must re-build the bootloader with the feature disabled.
     18 * Laguna bootloader
     19  - see [wiki:laguna/bootloader] for building
     20  - alter config
     21(include/configs/cavium_cns3000.h and/or include/configs/cavium_cns3000_spi.h):
     22   * remove '#define CONFIG_CNS3000_SERIAL'
     23   * set CONFIG_BOOTDELAY to 0 to save a couple of seconds on bootup
     24 * Ventana bootloader
     25  - see [wiki:ventana/bootloader] for building
     26  - alter config (include/configs/gw_ventana.h):
     27   * remove '#define CONFIG_DM_SERIAL'
     28   * set CONFIG_BOOTDELAY to 0 to save a couple of seconds on bootup
     29
     30
     31[=#kernel]
     32== Disable Kernel serial console ==
     33In order to disable serial console for the Linux Kernel you can either recompile it with the support disabled, or you can alter the bootargs the bootloader passes to the kernel to disable it at runtime.
     34
     35Kernel configuration:
     36 * Remove the following from the kernel config (.config)
     37  * CONFIG_SERIAL_CORE_CONSOLE
     38  * CONFIG_SERIAL_EARLYCON
     39  * CONFIG_SERIAL_IMX_CONSOLE (Ventana / imx6)
     40  * CONFIG_SERIAL_8250_CONSOLE (Laguna / cns3xxx)
     41
     42Kernel bootargs:
     43 * Remove the 'console' bootargs
     44
     45Example bootloader configuration to remove the {{{console}}} bootarg:
     46 * Laguna - Alter {{{bootargs}}}:
     47{{{
     48printenv bootargs
     49bootargs=console=ttyS0,115200 root=/dev/mtdblock3 rootfstype=squashfs,jffs2 noinitrd init=/etc/preinit
     50setenv bootargs 'root=/dev/mtdblock3 rootfstype=squashfs,jffs2 noinitrd init=/etc/preinit'
     51saveenv
     52}}}
     53 * Ventana - unset {{{console}}}:
     54{{{
     55setenv console
     56saveenv
     57}}}
     58
     59
     60
     61[=#linuxos]
     62== Disable Linux OS console login ==
     63In order to disable console login in a Linux OS you must disable the service that performs this function. While this is Linux distribution specific it usually involves the 'init' process launching the 'getty' or 'login' application with a parameter of a specific serial device or tty1 (which is the kernel console tty)
     64
     65=== OpenWrt ===
     66modern OpenWrt uses it's own {{{procd}}} as a replacement for the standard Linux init. While it is a complete re-implementation it still follows the standard of processing an {{{/etc/inittab}}} file for configuring what processes are spawned from init.
     67
     68To kill off login from the kernel serial console as well as any other serial devices, remove or comment with a leading '#' any lines that invoke {{{/bin/ash --login}}} from /etc/inittab such as:
     69{{{
     70::askconsole:/bin/ash --login
     71tty1::askfirst:/bin/ash --login
     72}}}
     73
     74=== Yocto (and other Linux distros using the standard sysvinit) ===
     75Many Linus distros use the {{{sysvinit}}} package which processes {{{/etc/inittab}}} for commands to spawn a {{{getty}}} on various serial devices or tty's.
     76
     77To kill off login from the kernel serial console as well as any other serial devices, remove or comment with a leading '#' any lines that invoke the {{{getty}}} process from /etc/inittab. For example, remove the following:
     78{{{
     79mxc1:12345:respawn:/sbin/getty -L 115200 ttymxc1
     801:12345:respawn:/sbin/getty 38400 tty1
     81}}}
     82
     83=== Ubuntu ===
     84Ubuntu doesn't by default enable serial console or serial port login capability however if you have added this it may have been done by adding an {{{/etc/init/serial.conf}}} that you can alter or remove.