22.214.171.124.2. Command Options
Command options instruct
iptablesto perform a specific action. Only one command option is allowed per
iptablescommand. With the exception of the help command, all commands are written in upper-case characters.
iptablescommand options are as follows:
-A— Appends the rule to the end of the specified chain. Unlike the
-Ioption described below, it does not take an integer argument. It always appends the rule to the end of the specified chain.
-D <integer> | <rule>— Deletes a rule in a particular chain by number (such as
5for the fifth rule in a chain), or by rule specification. The rule specification must exactly match an existing rule.
-E— Renames a user-defined chain. A user-defined chain is any chain other than the default, pre-existing chains. (Refer to the
-Noption, below, for information on creating user-defined chains.) This is a cosmetic change and does not affect the structure of the table.
NoteIf you attempt to rename one of the default chains, the system reports a
Match not founderror. You cannot rename the default chains.
-F— Flushes the selected chain, which effectively deletes every rule in the chain. If no chain is specified, this command flushes every rule from every chain.
-h— Provides a list of command structures, as well as a quick summary of command parameters and options.
-I [<integer>]— Inserts the rule in the specified chain at a point specified by a user-defined integer argument. If no argument is specified, the rule is inserted at the top of the chain.
ImportantAs noted above, the order of rules in a chain determines which rules apply to which packets. This is important to remember when adding rules using either the
-Ioption.This is especially important when adding rules using the
-Iwith an integer argument. If you specify an existing number when adding a rule to a chain,
iptablesadds the new rule before (or above) the existing rule.
-L— Lists all of the rules in the chain specified after the command. To list all rules in all chains in the default
filtertable, do not specify a chain or table. Otherwise, the following syntax should be used to list the rules in a specific chain in a particular table:
-t<table-name>Additional options for the
-Lcommand option, which provide rule numbers and allow more verbose rule descriptions, are described in Section 126.96.36.199.6, “Listing Options”.
-N— Creates a new chain with a user-specified name. The chain name must be unique, otherwise an error message is displayed.
-P— Sets the default policy for the specified chain, so that when packets traverse an entire chain without matching a rule, they are sent to the specified target, such as ACCEPT or DROP.
-R— Replaces a rule in the specified chain. The rule's number must be specified after the chain's name. The first rule in a chain corresponds to rule number one.
-X— Deletes a user-specified chain. You cannot delete a built-in chain.
-Z— Sets the byte and packet counters in all chains for a table to zero.