[CentOS] /etc/inittab: Serial access/ Console Server

Warren Crigger

warren at leetnet.com
Sat Jul 1 01:42:32 UTC 2006


Very good info...although at my company we manage our AIX and Linux servers
with advocent/kvm when ssh is not an option.  At home, this may come in
handy!  Thanks!

> -----Original Message-----
> From: centos-bounces at centos.org 
> [mailto:centos-bounces at centos.org] On Behalf Of 
> pctech at mybellybutton.com
> Sent: Friday, June 30, 2006 1:11 PM
> To: centos at centos.org
> Subject: RE: Re: [CentOS] /etc/inittab: Serial access/ Console Server
> 
> >On Thu, 2006-06-29 at 20:48 -0700, Chris Fox wrote:
> >> -----BEGIN PGP SIGNED MESSAGE-----
> >> Hash: SHA1
> >>  
> >> Rodrigo Barbosa wrote:
> >> 
> >> > you might want to try agetty:
> >> >
> >> > T0:23:respawn:/sbin/agetty 9600 ttyS0 vt100
> >> >
> >> > Not sure if it will work, but seems likely.
> >> >
> >> I've always wanted to know how this is done (before serial 
> ports go 
> >> away forever).
> >> 
> >
> >We (CentOS Project) just got a $29,000 machine w/o a video 
> card. (Sparc 
> >niagara t2000 machine).
> >
> >I use a serial connection to what it boot ...
> >
> >
> 
> You don't just need the inittab setting.  You also need a 
> GRUB setting and a secureTTY detting.  The following is a 
> paste out of my firewall document that I wrote that has been 
> tested and works:
> 
> 6.15	Configuring Headless Operation
> By configuring "headless" operating we will be able to manage 
> the firewall via a cable plugged into the serial port of the 
> firewall.  This obviates the need to plug a keyboard and 
> monitor into it to perform changes.  Thus the term "headless".
> 
> 6.15.1	Changes to /etc/inittab
> The /etc/inittab file contains settings that get applied to 
> the Operating Systems at boot time.  There are some changes 
> that need to be made to these settings.  In order to edit the 
> /etc/inittab file type:
> 
> vi /etc/inittab
> 
> Typing this command will open the /etc/inittab file for editing.
> 
> As stated earlier the 18th line down is the run level line. 
> Add the following line to the file:
> 
> S0:12345:respawn:/sbin/agetty ttyS0 9600 linux
> 
> This line sets the Operating System to be able to send boot 
> time information to the serial port in addition to the console.
> 
> After you have made these changes to the /etc/inittab file 
> press the colon (: ) key and then type wq to quit vi and save 
> the changes. 
> 
> 6.15.2	Changes to /etc/securetty
> The /etc/securetty sets the controls for which TTY devices 
> that the root account can log on via.  In order for us to be 
> able to log onto the serial console as root or to be able to 
> su to root we must add a line to the file.  In order to edit 
> the /etc/secuertty file type:
> 
> vi /etc/securetty
> 
> Typing this command will open the /etc/secuertty file for editing.
> 
> Add the following line to the end of the file:
> 
> ttyS0
> 
> This line sets the Operating System to allow root to log on 
> to the serial port in addition to the console.
> 
> After you have made these changes to the /etc/securetty file 
> press the colon (: ) key and then type wq to quit vi and save 
> the changes.
> 
> 6.15.3	Changes to the Boot Loader
> In order for boot-time messages to be sent to the console, 
> including the boot loader information some changes must be 
> made to the configuration file for it.  The boot loader that 
> CentOS uses is GRUB.  As such, the configuration file is 
> /etc/grub.conf.
> 
> The first change that we must make is to add some lines after 
> the timeout line in the GRUB configuration file.  In order to 
> edit the /etc/grub.conf file type:
> 
> vi /etc/grub.conf
> 
> Typing this command will open the /etc/grub.conf file for editing.
> 
> Add the following two lines after the timeout line in the 
> configuration file:
> 
> serial --unit=0 --speed=9600
> terminal --timeout=2 serial console
> 
> Another change that we must make in the GRUB configuration 
> file is to tell the kernel to send out all kernel-level 
> messages to the serial port in addition to the console.  That 
> is done by adding the following line to the end of the kernel line:
> 
> console=tty1 console=ttyS0,9600
> 
> After you have made these changes to the /etc/grub.conf file 
> press the colon (: ) key and then type wq to quit vi and save 
> the changes.
> 
> Once you have made these changes reboot the firewall by 
> typing by typing:
> 
> reboot
> 
> The firewall will now reboot.
> 
> 
> 
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