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Old 01-11-2016, 02:20 AM   #1
aristosv
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resolv.conf on a read-only operating system


I am working on configuring Raspbian jessie to run as read-only. The only part of the file system that will be writable is /tmp which is mounted as tmpfs. DHCP is configured to write everything in /tmp so the system gets an IP Address from DHCP.

My problem is that the system cannot write to /etc/resolv.conf. I can ping internet IP Addresses, but not domain names. Theres no resolution.

I have created a symbolic link, pointing /etc/resolv.conf to /tmp/resolv.conf. But the issue here is that everything in /tmp is deleted on every boot. And resolv.conf is not created automatically. So theres no file for the system to write to.

I have also tried creating /tmp/resolv.conf using touch /tmp/resolv.conf in /etc/rc.local. The file gets created but theres nothing written in it. When I run dhclient manually after the system has booted, it writes to /tmp/resolv.conf and everything is fine. So I added the command dhclient in /etc/rc.local but it didnt write anything in /tmp/resolv.conf

Im kind of lost here. I need a tidy, proper way of moving resolv.conf to /tmp

Last edited by aristosv; 01-11-2016 at 02:21 AM.
 
Old 01-11-2016, 08:45 AM   #2
pingu_penguin
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If your nameservers are not going to change , then perhaps you could try adding the following to /etc/rc.local :

# echo "nameserver x.x.x.x" > /tmp/resolv.conf
# echo "nameserver y.y.y.y" >> /tmp/resolv.conf

where x.x.x.x and y.y.y.y and the nameservers required.

hope this helps.

Also , Is your Raspbian Jessie getting only an IP via dhcp and not the nameservers ? posting your rc.local could help a bit too.

Regards,
pingu.
 
Old 01-11-2016, 08:55 AM   #3
aristosv
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The name servers are going to be changing.

IP and DNS information all exist in /etc/network/interfaces. But unless /etc/resolv.conf has the DNS information, I don't have internet access.
 
Old 01-11-2016, 09:07 AM   #4
pingu_penguin
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In that case you could add the following to your /etc/network/interfaces file :

auto eth0
iface eth0 inet dhcp

where I presume eth0 is the nic in your device.
 
Old 01-11-2016, 09:19 AM   #5
aristosv
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Maybe I wasn't clear.
The system gets an IP Address from DHCP. That part is working OK.
The problem is with resolv.conf not containing any DNS server entries, because the file system is read-only.
So I need to somehow move /etc/resolv.conf to /tmp which is writeable, but emptied on each reboot.
 
Old 01-11-2016, 10:00 AM   #6
pingu_penguin
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Hi,

Sorry for the confusion.

The dhclient command invokes the /sbin/dhclient-script from time to time (man dhclient-script) in debian.
Perhaps you could replace the path for /etc/resolv.conf to /tmp/resolv.conf in the script and then give it a try.

ie.
1.modify the /sbin/dhclient-script script.
2. modify /etc/rc.local to contain the following (order matters obv.) :
# touch /tmp/resolv.conf
# dhclient <interface>

Make sure you backup the /sbin/dhclient-script script to a safe place before modifying it.

Hope this helps.

Regards,
pingu.
 
Old 01-12-2016, 02:26 AM   #7
aristosv
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Modifying dhclient-script did it. Thank you.
 
  


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