Provided by: libpam-abl_0.6.0-5_amd64 bug


       pam_abl.conf - Configuration file for pam_abl PAM module.


       Configuration file for both the pam_abl(8) PAM module, and the pam_abl(1) command line


           word        ::= /[^\s\|\/\*]+/
           name        ::= word | '*'
           username    ::= name
           servicename ::= name
           userservice ::= username
                       |   username '/' servicename
           namelist    ::= userservice
                       |   userservice '|' namelist
           userspec    ::= namelist
                       |   '!' namelist
           multiplier  ::= 's' | 'm' | 'h' | 'd'
           number      ::= /\d+/
           period      ::= number
                       |   number multiplier
           trigger     ::= number '/' period
           triglist    ::= trigger
                       |   trigger ',' triglist
           userclause  ::= userspec ':' triglist
           rule        ::= userclause
                       |   userclause /\s+/ rule

   Rule syntax
       Each rule consists of a number of space separated user clauses. A user clause specifies
       the user (and service) names to match and a set of triggers. A simple example would be


       which means block any user () if they are responsible for ten or more failed
       authentication attempts in the last hour. In place of the  which matches any user a list
       of usernames can be supplied like this


       which means block the users root, dba and admin if they are responsible for ten or more
       failed authentication attempts in the last hour. You can also specify a service name to
       match against like this


       which means block the users root for service 'sshd and dba for any service if they are
       responsible for three or more failed authentication attempts in the last day'. Finally you
       can specify multiple triggers like this


       which means 'block the user root if they are responsible for ten or more failed attempts
       in the last hour or twenty or more failed attempts in the last day.

       Multiple rules can be provided separated by spaces like this

           *:10/1h root:5/1h,10/1d

       in which case all rules that match a particular user and service will be checked. The user
       or host will be blocked if any of the rule triggers matches. The sense of the user
       matching can be inverted by placing a ! in front of the rule so that


       is a rule which would match for all users apart from root. It is important to treat root
       as a special case in the user_rule otherwise excessive attempts to authenticate as root
       will result in the root account being locked out even for valid holders of root
       credentials. The config file can contain any arguments that would be supplied via PAM
       config. In the config file arguments are placed on separate lines. Comments may be
       included after a # and line continuation is possible by placing a back slash at the end of
       the line to be continued. Here is a sample /etc/security/pam_abl.conf:

           # /etc/security/pam_abl.conf

       All of the standard PAM arguments (debug, expose_account, no_warn, try_first_pass,
       use_first_pass, use_mapped_pass) are accepted; with the exception of debug and no_warn
       these are ignored.

       The arguments that are specific to the PAM module are as follows:

           Specify the directory where the Berkeley db can store it’s lock and log files. Make
           sure this dir exists and is writable.

           It’s value should have the following syntax "<minimum>-<maximum>". If you do not block
           machines that do too many attempts, the db can easily become bloated. To prevent this
           we introduced this setting. As soon as there are a <maximum> number of attempts for a
           user/host, the number of stored attempts for this user/host is reduced to <minimum>. A
           <maximum> of 0 means no limits. Make sure that <minimum> is larger then any rule
           specified. We recommend a value of "1000-1200".

       host_db, user_db
           Specify the name of the databases that will be used to log failed authentication
           attempts. The host database is used to log the hostname responsible for a failed auth
           and the user database is used to log the requested username. If host_db or user_db is
           omitted the corresponding auto blacklisting will be disabled.

       host_purge, user_purge
           Specify the length of time for which failed attempts should be kept in the databases.
           For rules to work correctly this must be at least as long as the longest period
           specified in a corresponding rule. You may wish to retain information about failed
           attempts for longer than this so that the pam_abl command line tool can report
           information over a longer period of time. The format for this item is a number with an
           optional multiplier suffix, s, m, h or d which correspond with seconds, minutes, hours
           and days. To specify seven days for example one would use 7d. Note that in normal
           operation pam_abl will only purge the logged data for a particular host or user if it
           happens to be updating it, i.e. if that host or user makes another failed attempt. To
           purge all old entries the pam_abl command line tool should be used.

       host_rule, user_rule
           These are the rules which determine the circumstances under which accounts are
           auto-blacklisted. The host_rule is used to block access to hosts that are responsible
           for excessive authentication failures and the user_rule is used to disable accounts
           for which there have been excessive authentication failures. The rule syntax is
           described in full below.

       host_clr_cmd, host_blk_cmd, user_clr_cmd, user_blk_cmd
           Deprecated for security reasons. Please use the corresponding safer option:
           host_clear_cmd, host_block_cmd, user_clear_cmd, user_block_cmd

       host_clear_cmd, host_block_cmd, user_clear_cmd, user_block_cmd
           These specify commands that will run during a check when an item switches state since
           its last check.

           host_clear_cmd and user_clear_cmd will run if the host or user is currently allowed
           access. host_block_cmd and user_block_cmd are run if the host or user is currently
           being blocked by their respective rules.

           Within the commands, you can specify substitutions with %h, %u and %s, which will be
           replace with the host name, user name and service currently being checked. For
           security reasons we do not run the command using the system call. We use the more
           secure fork/exec solution. This means that you can’t specify input and output

           Note that this also means that no escaping is done, so if you call a shell here, you
           might introduce a security problem.

           The commands should follow a special syntax (you can use the command line tool with
           the -d option to test the parsing of your commands) where the command and it’s
           different arguments need to be enclosed in [] and all text not enclosed in [] is
           simply ignored. For example: "[/usr/bin/logger] ignored [block] [user] [%u]" will run
           the command "/usr/bin/logger block user <current user>". If you want to specify a [, ]
           or \, you need to escape them with a \.

       host_whitelist, user_whitelist
           ;-seperated list of hosts/users whose attempts will not be recorded. So if an attempt
           is made from "" for user "root" and "root" is in the whitelist, only an
           attempt for his machine is recorded. If a user is whitelisted, this does not prevent
           his machine from being blocked. Hosts can be specified using their IP ( or
           using a netmask (


           # /etc/security/pam_abl.conf
           host_block_cmd=[/sbin/iptables] [-I] [INPUT] [-s] [%h] [-j] [DROP]
           user_clear_cmd=[/usr/bin/logger] [block] [user] [%u]


       pam_abl.conf(5), pam_abl(1)


       Lode Mertens <>

       Andy Armstrong <>

       Chris Tasma <>


       Chris Tasma