iptables-apply

iptables-apply [options]

-t seconds
    Sets the timeout, in seconds, to wait before committing the rules. The default is 30 seconds.

-f filename
    Read from the given file. If not specified iptables-apply will try to read rules from standard input.

-w
    Wait forever. If specified, iptables-apply will wait indefinitely for user confirmation (Ctrl+C to abort).

-q
    Quiet mode. Suppress output of rule additions.

-v
    Verbose mode. Display more detailed information about the process.

-c
    Check mode. Parse the ruleset without applying it.

-n
    Numeric output. Show addresses and port numbers in numeric format.

-h
    Display a help message and exit.

iptables-apply is a utility to test a new iptables ruleset before applying it. It reads a set of iptables rules from standard input, applies them temporarily, and then waits for a specified amount of time. If no errors occur during this time, the rules are made permanent. If errors occur, or the timeout expires, the rules are rolled back to the previous state. This helps to prevent accidental lockouts due to misconfigured firewall rules.

The primary purpose of iptables-apply is to provide a safer way to modify iptables rules in a production environment. Without it, a single typo in a firewall rule can lead to a server becoming inaccessible. Iptables-apply greatly reduces this risk by verifying the ruleset before making it persistent.

If iptables-apply is interrupted unexpectedly (e.g., by a power outage), the iptables configuration may be left in a partially applied state. Always test in a non-production environment before deploying to production.

The typical workflow involves generating a new set of iptables rules (often using iptables-save and then editing the output), and then piping this new ruleset into iptables-apply. Iptables-apply then applies these rules temporarily, gives you a specified time period to test them, and if you don't interrupt, commits them. Otherwise they are automatically reverted to the original rules.

When iptables-apply rolls back rules after a timeout or interruption, it attempts to restore the previous iptables configuration. However, it is possible that the rollback could fail, for instance, if the original rules have been altered outside of iptables-apply during the test period. It's essential to have backups or other recovery mechanisms in place.

The iptables-apply command was created to address the need for safer iptables configuration management, providing a mechanism to test and rollback rule changes. It is commonly used by system administrators to avoid locking themselves out of servers when modifying firewall rules.

iptables(8), ip6tables(8), iptables-save(8), iptables-restore(8)