When The System Get The Hostname

angleeye

hi,
please help .
I am using redhat9.0.
I removed the line 'DOMAINNAME=localdomain' from /etc/sysconfig/network.
then after a reboot, the hostname change to 'unassigned'.
how could it be.  

is anybody know:
which is the file we are using to store the machine`s name?
and when it is read to set up the hostname ?I mean which step at start time.

by the way, I tried to use 'hostname' to rename my machine, it work fine.
is this the way used in the start time?

if you know these ,please stop me wonderring.

thanks a lot.

t920

给你移到linux版了～～～

wind521

please check /etc/hosts

wolfg

add HOSTNAME=yourhostname to /etc/sysconfig/network

q1208c

I think the "hostname" should setup with the init script "sysinit",

you can check the /etc/rc.d/sysinit for more information.

and the hostname is stored is /etc/sysconfig/network
like this "HOSTNAME=localhost.localdomain"

the hostname in /etc/hosts only indecate that the ip address of the localhost, maybe an other hostname.

wolfg

原帖由 "q1208c" 发表：
I think the "hostname" should setup with the init script "sysinit",

you can check the /etc/rc.d/sysinit for more information.

and the hostname is stored is /etc/sysconfig/network
like this "..........

exactly the file is /etc/rc.d/rc.sysinit

I checked this file and found this

1. 
   
2. HOSTNAME=`/bin/hostname`
   
3. HOSTTYPE=`uname -m`
   
4. unamer=`uname -r`
   
5. eval version=`echo $unamer | awk -F '.' '{ print "(" $1 " " $2 ")" }'`
   
6. 
   
7. if [ -f /etc/sysconfig/network ]; then
   
8.     . /etc/sysconfig/network
   
9. fi
   
10. if [ -z "$HOSTNAME" -o "$HOSTNAME" = "(none)" ]; then
    
11.     HOSTNAME=localhost
    
12. fi
    
13. 
    

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q1208c

[quote]原帖由 "wolfg"][/quote 发表：


Thanks.    

wolfg

原帖由 "q1208c" 发表：


Thanks.    

I just wonder how the command 'hostname' get the hostname or where it save the hostname to?

angleeye

thanks everybody,
after the discussion, I think I got the point. ,even I have not look the sysinit yet.I will check it later.

you help me a lot. I love CU.

more, I found these to share you.

http://lxr.linux.no/source/kernel/sys.c?v=1.0.9#654
sys_sethostname
http://lxr.linux.no/source/include/linux/utsname.h?v=1.0.9#L33
system_utsname

and here comes anther question:

1. 
   
2. Function: long int gethostid (void)
   
3. 
   
4. This function returns the Internet address of the machine the program is running on.
   
5. 
   
6. Function: int sethostid (long int id)
   
7. 
   
8. The sethostid function sets the address of the host machine to id. Only privileged processes are allowed to do this. Usually it happens just once, at system boot time.
   
9. 
   
10. The return value is 0 on success and -1 on failure. The following errno error condition is defined for this function:
    

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I found these in GNU C Library document .
you know these functions? does we need to set the IP address at start time? Is there two correspond system functions the above two funcs call on? If it is ,why I can not found them?If not , so when and how we will use them?


thanks again!

wolfg

http://www.linuxforum.net/books/LinuxFAQ/common-sys-v-init.html

according this document, when booting, the init process will read /etc/inittab first, then it found script for system initialization
si::sysinit:/etc/rc.d/rc/rc.sysinit
(This maybe varies from distribution of linux)

when rc.sysinit be executing, it gets HOSTNAME from /etc/sysconfig/network (if not set in the file, use localhost) and uses following scripts to set the hostname

1. 
   
2. update_boot_stage RChostname
   
3. action $"Setting hostname ${HOSTNAME}: " hostname ${HOSTNAME}
   

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and I think the command 'hostname' save the value in /proc/sys/kernel/hostname

1. 
   
2. # hostname
   
3. foo
   
4. # cat /proc/sys/kernel/hostname
   
5. foo
   
6. # hostname foobar
   
7. # cat /proc/sys/kernel/hostname
   
8. foobar
   
9. # echo "bar" >; /proc/sys/kernel/hostname
   
10. # hostname
    
11. bar
    

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but after you reboot, the server's hostname is still the original one    "foo" because we didn't modify /etc/sysconfig/network.