This might sound like a silly idea, but if the users aren't actually doing anything, you could do:
cat /etc/passwd | cut -f 1 -d : >/tmp/users.list
Then edit /tmp/users.list to only contain the users you want. Then do:
for i in `cat /tmp/users.list`
do
userdel $i
useradd -m $i
done
However, many Redhat based distributions will create you a new home directory when you first login, providing it is specified in /etc/passwd where the directory should be.
To test that, do an "su - " and see if it does "the right thing". If it doesn't, the above script will work quite nicely, I think.
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
When you are creating an account to run a daemon, service, or other system software, rather than an account for interactive use.
Technically, it makes no difference, but in the real world it turns out there are long term benefits in keeping user and software accounts in separate parts of the numeric space.
Mostly, it makes it easy to tell what the account is, and if a human should be able to log in.