To use xauth selectively, as user1 run:
xauth list|grep `uname -n`
This prints the hexkey authorization entries for you . You could have different displays associated with those hosts as well.
As user2 set your display (assuming default case):
DISPLAY=:0; export DISPLAY
Then run:
xauth add $DISPLAY . hexkey
Note the dot after the $DISPLAY and before the hexkey.
When access is no longer needed, as user2 you can run:
xauth remove $DISPLAY
Short answer: you can't. Ports below 1024 can be opened only by root. As per comment - well, you can, using CAP_NET_BIND_SERVICE, but that approach, applied to java bin will make any java program to be run with this setting, which is undesirable, if not a security risk.
The long answer: you can redirect connections on port 80 to some other port you can open as normal user.
Run as root:
# iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 8080
As loopback devices (like localhost) do not use the prerouting rules, if you need to use localhost, etc., add this rule as well (thanks @Francesco):
# iptables -t nat -I OUTPUT -p tcp -d 127.0.0.1 --dport 80 -j REDIRECT --to-ports 8080
NOTE: The above solution is not well suited for multi-user systems, as any user can open port 8080 (or any other high port you decide to use), thus intercepting the traffic. (Credits to CesarB).
EDIT: as per comment question - to delete the above rule:
# iptables -t nat --line-numbers -n -L
This will output something like:
Chain PREROUTING (policy ACCEPT)
num target prot opt source destination
1 REDIRECT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:8080 redir ports 8088
2 REDIRECT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 redir ports 8080
The rule you are interested in is nr. 2, so to delete it:
# iptables -t nat -D PREROUTING 2
Best Answer
Like zed said but you probably have service running which mean that it if you do this, these services will not be able to read theses files either if the service doesn't run under the user permission, which is rarely the case, most service runs under their own users.
ACL (Access control list) are what you may need. Here is the official doc http://centos.org/docs/5/html/Deployment_Guide-en-US/ch-acls.html
Follow the documentation by editing the /etc/fstab and remounting the partition then simply
o for others, u for users.
Now retreive the acl :
I recommend you read the docs and do some tests. Hope this helped.