Can I create a user-specific hosts file to complement /etc/hosts?

Question

Is it possible to add a list of hosts that are only specific to a certain user? Perhaps a user-specific hosts file?

This mechanism should also complement the entries in the /etc/hosts file.

Answer 1

As far as I know there isn't. The easiest way to do what I think you want is to write an LD_PRELOAD library that overrides gethostbyname() and related functions.

Answer 2

Beside the LD_PRELOAD tricks. A simple alternative that may work on a few systems would be to binary-edit a copy of the system library that handles hostname resolution to replace /etc/hosts with a path of your own.

For instance, on Linux:

If you're not using nscd, copy libnss_files.so to some location of your own like:

mkdir -p -- ~/lib &&
cp /lib/x86_64-linux-gnu/libnss_files.so.2 ~/lib

Binary-edit the copy to replace /etc/hosts in there to something the same length like /tmp/hosts.

perl -pi -e 's:/etc/hosts:/tmp/hosts:g' ~/lib/libnss_files.so.2

Edit /tmp/hosts to add the entry you want. And use

export LD_LIBRARY_PATH=~/lib

for nss_files to look in /tmp/hosts instead of /etc/hosts.

Instead of /tmp/hosts, you could also make it /dev/fd//3, and do

exec 3< ~/hosts

For instance which would allow different commands to use different hosts files.

If nscd is installed and running, you can bypass it by doing the same trick, but this time for libc.so.6 and replace the path to the nscd socket (something like /var/run/nscd/socket) with some nonexistent path.

Answer 3

Not sure if this would help you, but I came here looking for a way to add saved "hosts" somewhere that was easily accessible to only my user.

I basically needed to be able to ssh into certain boxes on our work network, which only has one entry point.

What I did was add alias's to my .bashrc file.

For example, if you added:

alias jrfbox 'ssh jason@1912.168.6.6'

at the bottom of the ~/.bashrc (~ is your home directory), then after you logout and login again, you can type "jrfbox" hit enter, and it will connect.

Answer 4

AFAIK, There is nothing like that, and there is no reason to have something like that. There is a design problem if an admin think that he need a hosts file per user. Think about it: You can't hide a host just because you don't have it in /etc/hosts, you're reading more files when the system is initialized and maybe the difference between 2 users will be up to 5 hosts.

The right question is: Is there a good reason to want something like that?

Maybe the answer will say what kind of utility you really want

EDIT - Maybe this is a good conclusion: if you use your own domain as a domain name server (in DNS), you have just 1 table to map domains in the server. DNS does not work at user-level.