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
This was a messy problem.
I ended up adding all the users to the crontab group, and setting the group ownership of all needed files to that crontab group.
A lot of permissions were messed up. Changing the group ownership to something else first "resets" those permissions.
The crontab executable:
sudo chgrp crontab /usr/bin/crontab
sudo chmod g+s /usr/bin/crontab
Result: -rwxrwsr-x 1 root crontab 37K 2010-04-15 08:51 /usr/bin/crontab
The cron spool files:
sudo chmod 4774 -R /var/spool/cron
Result: drwsrwsr-- 5 root crontab 4,0K 2009-12-23 23:01 cron
The cron files in these spool directories need to be READ AND WRITE only. Otherwise they won't run.
sudo chmod 600 /var/spool/cron/crontabs/*
The cron pid file:
sudo chmod 744 /var/run/crond.pid
I think that should cover it.
Best Answer
You're probably in a directory that can't be written to, such as
/proc, or an NFS mounted directory withroot_squash. Change to a writable directory and try again, or direct your output file to a writable directory.