Ubuntu Manpage: firehol - an easy to use but powerful iptables stateful firewall

NAME

       firehol - an easy to use but powerful iptables stateful firewall

SYNOPSIS

       firehol

       sudo -E firehol panic [ IP ]

       firehol command [ – conf-arg...  ]

       firehol CONFIGFILE [start|debug|try] [– conf-arg...  ]

DESCRIPTION

Running firehol invokes iptables(8) to manipulate your firewall.

Run without any arguments, firehol will present some help on usage.

When given CONFIGFILE, firehol will use the named file instead of /etc/firehol/firehol.conf as its con‐
figuration. If no command is given, firehol assumes try.

It is possible to pass arguments for use by the configuration file separating any conf-arg values from
the rest of the arguments with --. The arguments are accessible in the configuration using standard
bash(1) syntax e.g. $1, $2, etc.

PANIC
To block all communication, invoke firehol with the panic command.

FireHOL removes all rules from the running firewall and then DROPs all traffic on all iptables(8) tables
(mangle, nat, filter) and pre-defined chains (PREROUTING, INPUT, FORWARD, OUTPUT, POSTROUTING).

DROPing is not done by changing the default policy to DROP, but by adding one rule per table/chain to
drop all traffic. This allows systems which do not reset all the chains to ACCEPT when starting to func‐
tion correctly.

When activating panic mode, FireHOL checks for the existence of the SSH_CLIENT shell environment vari‐
able, which is set by ssh(1). If it finds this, then panic mode will allow the established SSH connec‐
tion specified in this variable to operate.

Note

In order for FireHOL to see the environment variable you must ensure that it is preserved. For
sudo(8) use the -E and for su(1) omit the - (minus sign).

If SSH_CLIENT is not set, the IP after the panic argument allows you to give an IP address for which all
established connections between the IP address and the host in panic will be allowed to continue.

COMMANDS

start; restart
Activates the firewall using /etc/firehol/firehol.conf.

Use of the term restart is allowed for compatibility with common init implementations.

try Activates the firewall, waiting for the user to type the word commit. If this word is not typed
within 30 seconds, the previous firewall is restored.

stop Stops a running iptables(8) firewall by clearing all of the tables and chains and setting the de‐
fault policies to ACCEPT. This will allow all traffic to pass unchecked.

condrestart
Restarts the FireHOL firewall only if it is already active. This is the generally expected behav‐
iour (but opposite to FireHOL prior to 2.0.0-pre4).

status Shows the running firewall, using /sbin/iptables -nxvL | less.

save Start the firewall and then save it using iptables-save(8) to the location given by FIREHOL_AU‐
TOSAVE. See firehol-defaults.conf(5) for more information.

The required kernel modules are saved to an executable shell script /var/spool/fire‐
hol/last_save_modules.sh, which can be called during boot if a firewall is to be restored.

Note

External changes may cause a firewall restored after a reboot to not work as intended where
starting the firewall with FireHOL will work.

This is because as part of starting a firewall, FireHOL checks some changeable values. For
instance the current kernel configuration is checked (for client port ranges), and RPC
servers are queried (to allow correct functioning of the NFS service).

debug Parses the configuration file but instead of activating it, FireHOL shows the generated ipta‐
bles(8) statements.

explain
Enters an interactive mode where FireHOL accepts normal configuration commands and presents the
generated iptables(8) commands for each of them, together with some reasoning for its purpose.

Additionally, FireHOL automatically generates a configuration script based on the successful com‐
mands given.

Some extra commands are available in explain mode.

help Present some help

show Present the generated configuration

quit Exit interactive mode and quit

helpme; wizard
Tries to guess the FireHOL configuration needed for the current machine.

FireHOL will not stop or alter the running firewall. The configuration file is given in the stan‐
dard output of firehol, thus firehol helpme > /tmp/firehol.conf will produce the output in
/tmp/firehol.conf.

The generated FireHOL configuration must be edited before use on your systems. You are required
to take a number of decisions; the comments in the generated file will instruct you in the choices
you must make.

FILES

       /etc/firehol/firehol.conf

AUTHORS

       FireHOL Team; Original man page by Marc Brockschmidt.

FireHOL Reference                               Built 24 Jan 2024                                     firehol(1)