bootup sequence

Thread Tools Search this Thread
Top Forums UNIX for Dummies Questions & Answers bootup sequence
# 1  
Old 08-04-2009
bootup sequence

What is the boot up sequence in UNIX?
# 2  
Old 08-04-2009
Since UNIX covers so many platforms and systems and varieties its hard to give a better than vague answer. But I will bite the bullet and be vague for you.
  • The system automatically loads the bootloader. This is a small program with only one job, to find and load the operating system kernel. On PC's its always in the first sector of the hard drive, or the 'boot' sector.
  • The bootloader loads the kernel into memory and runs it.
  • In linux at least, the first thing the kernel does is detect a whole slew of system parameters and devices. This is similar to the process of loading a driver, except the drivers are built in and just need to be operated.
  • Next, it attempts to mount the root filesystem, since it can't do anything without one.
  • Lastly the kernel creates process number one, init, which runs the processes to prepare the rest of the system and start up all the services its is configured to for its particular runlevel, including all terminal logins etc.
This is the simple way. Sometimes instead of a root filesystem, the bootloader gives the kernel a glob of memory containing files loaded from disk, which it may use to load extra drivers etc. before it mounts the real root filesystem overtop of it.
# 3  
Old 08-05-2009
Adding on to what Corona said, many systems' init process will include a line to start a shell script. In Linux, this is:

In Solaris 10 this is:

Then there is the concept of "init level". This allows one to start the operating system with a different startup-configuration. If you start with init level 3 in Linux, the inittab checks for the line:
l3:3:wait:/etc/rc.d/rc 3

and then runs the script /etc/rc.d/rc with parameter "3". This rc script then in turn looks into the /etc/rc.d/rc3.d directory and runs all the scripts (in lexicographical order) starting with the letter S. (There are more steps here, but I'm giving you the basics).
Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. SCO

Error F painit on bootup

I have a known good external SCSI HD running SCO UNIX OpenServer 5.0.7. I decided that I wanted to be able to run this drive on another computer, so I bought the same SCSI card as before (LSI) and then attempted to boot on the other system. The bootup process hung with the error F painit. I've... (13 Replies)
Discussion started by: Transpower
13 Replies

2. Shell Programming and Scripting

find common entries and match the number with long sequence and cut that sequence in output

Hi all, I have a file like this ID 3BP5L_HUMAN Reviewed; 393 AA. AC Q7L8J4; Q96FI5; Q9BQH8; Q9C0E3; DT 05-FEB-2008, integrated into UniProtKB/Swiss-Prot. DT 05-JUL-2004, sequence version 1. DT 05-SEP-2012, entry version 71. FT COILED 59 140 ... (1 Reply)
Discussion started by: manigrover
1 Replies

3. Solaris

Sunfire X4600 Errors on Bootup

Hi Folks, Has anyone seen these errors on bootup. Mar 15 12:22:30 svc.startd: svc:/system/device/local:default: Method "/lib/svc/method/devices-local" failed due to signal (c) 1983, 2010, Oracle and/or its affiliates. All rights reserved. Configuring devices. ... (1 Reply)
Discussion started by: ESSTEAM
1 Replies

4. UNIX for Advanced & Expert Users

system slows after bootup for some time

Hi, I am using a Linux system running at run level 3. I am finding a wired problem, once the system boots, the system terminal slows down, I need to type the characters repeatedly to enter my login and password info. Also running any commands takes time, it stays in this condition for some... (1 Reply)
Discussion started by: cjjoy
1 Replies

5. AIX

File system not mounting at bootup

Hi, I've got a recent problem with 2 file systems on an AIX 5.3 server. The fs's are marked to auto mount at startup and do show as being mounted after a a restart however if you cd to the mount point and 'df -g .' it shows the fs hasn't actually mounted. $ mount |grep SQLT0001.0 ... (2 Replies)
Discussion started by: m223464
2 Replies

6. AIX

How to start ssh at bootup

Hi i installed ssh of version v 1.21 and my AIX is of 5.3. I want to start my ssh deamon at the startup can any one please help me out reg.. Thanks in advance.. (1 Reply)
Discussion started by: kmalla
1 Replies

7. UNIX for Dummies Questions & Answers

Why not automatic bootup

Evry time I start up my mavhine ,have to type in unix at Boot : Is there a way unix should bootup automatically? Asif (2 Replies)
Discussion started by: asif iqbal
2 Replies

8. UNIX for Dummies Questions & Answers

Bootup Error

Hi all The following error was displayed when a sco server (5.0.5) was booted. What should be done to overcome the problem. Replies appreciated. Bios 03.0 0130688 KB memory good 01 processor(s) in system remote console dialing on, please wait connect fail : modem off cpu clock... (6 Replies)
Discussion started by: raguramtgr
6 Replies

9. UNIX for Advanced & Expert Users

bootup script

Hello there I need to run a script whenever i reboot or startup my HP-UX server. This script adds some routes to the route table, and it start third party aplications like "Star Manager". I thought i could do this simply putting the script in "/sbin/init.d, and a link to the script in... (7 Replies)
Discussion started by: vascobrito
7 Replies

10. UNIX for Dummies Questions & Answers

Triple bootup

Hi guys, May I know how to install Solaris 8 in the way that I can triple boot it with my the other two OS: WIndows ME and Windows 2000 Pro. Can you all please kindly advise me on how to setup the triple boot process inorder to allow Windows ME to be the default OS when being ask to choose... (1 Reply)
Discussion started by: cia
1 Replies
Login or Register to Ask a Question