iptables-apply

iptables-apply [-t seconds] [-w wait-time] [-r] [-c test-command] [-x extension] [-V] [-h] [filename]

-t seconds
    Sets the rollback timeout in seconds. Default is 60. If set to 0, iptables-apply will wait for user input (Enter key) before committing the rules. If the timeout expires without confirmation or a successful test, rules are reverted.

-w wait-time
    Specifies the wait time in seconds for the iptables-restore or ip6tables-restore command to obtain the xtables lock. This helps prevent conflicts with other iptables operations.

-r
    Forces a rollback to the previously saved rules without attempting to apply new ones. This can be used to manually revert to a known good state.

-c test-command
    Executes the specified test-command after applying the new rules. If the command exits with a non-zero status (indicating failure), the rules are automatically reverted. This allows for custom connectivity or application health checks.

-x extension
    Specifies the extension to use, effectively choosing between iptables and ip6tables. For example, use -x ip6tables to apply rules for IPv6.

-V
    Displays the version information of the iptables-apply utility.

-h
    Shows a brief help message and usage instructions for the command.

filename
    The path to a file containing the new firewall rules to be applied. If this argument is omitted, iptables-apply will read the rules from standard input (stdin).

iptables-apply is a crucial utility for safely modifying Netfilter (iptables/ip6tables) firewall rulesets. Its primary function is to prevent administrators from inadvertently locking themselves out of a system when deploying new firewall configurations, a common risk during remote management.

The command operates by first saving the currently active rules. It then applies the new rules provided from a specified file or standard input. Crucially, after applying the new rules, iptables-apply initiates a timer, typically 60 seconds by default. During this period, an optional test-command can be executed to verify connectivity or rule functionality.

If the test-command succeeds, or if the timer expires without issues and no test was specified, the new rules are committed. However, if the test-command fails, or if the timer expires and iptables-apply detects a problem (e.g., loss of network access), it automatically reverts to the previously saved, functional ruleset. This automatic rollback mechanism provides a vital safety net, ensuring system accessibility even if the new rules are flawed. It's an indispensable tool for robust and secure firewall administration.

iptables-apply relies on the presence and proper functioning of iptables-save, iptables-restore, and their IPv6 counterparts. Severe system issues (e.g., kernel panic, power loss) that prevent script execution might still lead to an unrecoverable state. The robustness of the rollback largely depends on the reliability of the test-command if specified, or the default timeout mechanism's ability to detect connectivity loss. Be cautious when using rules that extensively flush tables, as this could interfere with the save/restore process if not properly managed by the script itself.

The core feature of iptables-apply is its intelligent rollback capability. If a specified test-command fails, or if the timeout is reached without user confirmation (when -t 0 is used) or successful implicit validation, the command automatically reverts to the previously saved, functional firewall ruleset. This crucial mechanism prevents unintended network isolation or system inaccessibility due to erroneous rule configurations.

New rules can be conveniently supplied to iptables-apply via standard input, allowing for dynamic rule generation and application from scripts or other commands. For example: cat rules.v4 | iptables-apply or generate_rules.sh | iptables-apply.

iptables-apply is a component of the broader iptables project, which provides the user-space tools for configuring the Linux kernel's Netfilter firewall. Its inception was driven by the practical need to enhance safety during firewall rule deployment, particularly for remote system administration. Before such utilities, applying new rules was a high-risk operation, as a misconfiguration could immediately sever network access. iptables-apply was developed to mitigate this risk by integrating a reliable rollback mechanism, reflecting a mature approach to system configuration management where safety and availability are paramount.

iptables(8), ip6tables(8), iptables-save(8), iptables-restore(8), netfilter(7)