Linux Certif

Toute la documentation sur la certification Linux LPI

auditd.conf

NAME

auditd.conf - audit daemon configuration file

DESCRIPTION

The file /etc/audit/auditd.conf contains configuration information specific to the audit daemon. It should contain one configuration keyword per line, an equal sign, and then followed by appropriate configuration information. The keywords recognized are: log_file, log_format, log_group, priority_boost, flush, freq, num_logs , disp_qos , dispatcher, name_format , name, max_log_file, max_log_file_action, space_left, action_mail_acct, space_left_action, admin_space_left, admin_space_left_action, disk_full_action, disk_error_action, tcp_listen_port, tcp_listen_queue, tcp_max_per_addr, use_libwrap, tcp_client_ports, tcp_client_max_idle, enable_krb5, krb5_principal, and krb5_key_file. These keywords are described below.

log_file

This keyword specifies the full path name to the log file where audit records will be stored. It must be a regular file.

log_format

The log format describes how the information should be stored on disk. There are 2 options: raw and nolog. If set to RAW, the audit records will be stored in a format exactly as the kernel sends it. If this option is set to NOLOG then all audit information is discarded instead of writing to disk. This mode does not affect data sent to the audit event dispatcher.

log_group

This keyword specifies the group that is applied to the log file's permissions. The default is root. The group name can be either numeric or spelled out.

priority_boost

This is a non-negative number that tells the audit daemon how much of a priority boost it should take. The default is 4. No change is 0.

flush

Valid values are none, incremental, data, and sync. If set to none, no special effort is made to flush the audit records to disk. If set to incremental, Then the freq parameter is used to determine how often an explicit flush to disk is issued. The data parameter tells the audit damon to keep the data portion of the disk file sync'd at all times. The sync option tells the audit daemon to keep both the data and meta-data fully sync'd with every write to disk.

freq

This is a non-negative number that tells the audit damon how many records to write before issuing an explicit flush to disk command. this value is only valid when the flush keyword is set to incremental.

num_logs

This keyword specifies the number of log files to keep if rotate is given as the max_log_file_action. If the number is < 2, logs are not rotated. This number must be 99 or less. The default is 0 - which means no rotation. As you increase the number of log files being rotated, you may need to adjust the kernel backlog setting upwards since it takes more time to rotate the files. This is typically done in /etc/audit/audit.rules.

disp_qos

This option controls whether you want blocking/lossless or non-blocking/lossy communication between the audit daemon and the dispatcher. There is a 128k buffer between the audit daemon and dispatcher. This is good enogh for most uses. If lossy is chosen, incoming events going to the dispatcher are discarded when this queue is full. (Events are still written to disk if log_format is not nolog.) Otherwise the auditd daemon will wait for the queue to have an empty spot before logging to disk. The risk is that while the daemon is waiting for network IO, an event is not being recorded to disk. Valid values are: lossy and lossless. Lossy is the default value.

dispatcher

The dispatcher is a program that is started by the audit daemon when it starts up. It will pass a copy of all audit events to that application's stdin. Make sure you trust the application that you add to this line since it runs with root privileges.

name_format

This option controls how computer node names are inserted into the audit event stream. It has the following choices: none, hostname, fqd, numeric, and user. None means that no computer name is inserted into the audit event. hostname is the name returned by the gethostname syscall. The fqd means that it takes the hostname and resolves it with dns for a fully qualified domain name of that machine. Numeric is similar to fqd except it resolves the IP address of the machine. User is an admin defined string from the name option. The default value is none.

name

This is the admin defined string that identifies the machine if user is given as the name_format option.

max_log_file

This keyword specifies the maximum file size in megabytes. When this limit is reached, it will trigger a configurable action. The value given must be numeric.

max_log_file_action

This parameter tells the system what action to take when the system has detected that the max file size limit has been reached. Valid values are ignore, syslog, suspend, rotate and keep_logs. If set to ignore, the audit daemon does nothing. syslog means that it will issue a warning to syslog. suspend will cause the audit daemon to stop writing records to the disk. The daemon will still be alive. The rotate option will cause the audit daemon to rotate the logs. It should be noted that logs with higher numbers are older than logs with lower numbers. This is the same convention used by the logrotate utility. The keep_logs option is similar to rotate except it does not use the num_logs setting. This prevents audit logs from being overwritten.

action_mail_acct

This option should contain a valid email address or alias. The default address is root. If the email address is not local to the machine, you must make sure you have email properly configured on your machine and network. Also, this option requires that /usr/lib/sendmail exists on the machine.

space_left

This is a numeric value in megabytes that tells the audit daemon when to perform a configurable action because the system is starting to run low on disk space.

space_left_action

This parameter tells the system what action to take when the system has detected that it is starting to get low on disk space. Valid values are ignore, syslog, email, exec, suspend, single, and halt. If set to ignore, the audit daemon does nothing. syslog means that it will issue a warning to syslog. Email means that it will send a warning to the email account specified in action_mail_acct as well as sending the message to syslog. exec /path-to-script will execute the script. You cannot pass parameters to the script. suspend will cause the audit daemon to stop writing records to the disk. The daemon will still be alive. The single option will cause the audit daemon to put the computer system in single user mode. halt option will cause the audit daemon to shutdown the computer system.

admin_space_left

This is a numeric value in megabytes that tells the audit daemon when to perform a configurable action because the system is running low on disk space. This should be considered the last chance to do something before running out of disk space. The numeric value for this parameter should be lower than the number for space_left.

admin_space_left_action

This parameter tells the system what action to take when the system has detected that it is low on disk space. Valid values are ignore, syslog, email, exec, suspend, single, and halt. If set to ignore, the audit daemon does nothing. Syslog means that it will issue a warning to syslog. Email means that it will send a warning to the email account specified in action_mail_acct as well as sending the message to syslog. exec /path-to-script will execute the script. You cannot pass parameters to the script. Suspend will cause the audit daemon to stop writing records to the disk. The daemon will still be alive. The single option will cause the audit daemon to put the computer system in single user mode. halt

disk_full_action

This parameter tells the system what action to take when the system has detected that the partition to which log files are written has become full. Valid values are ignore, syslog, exec, suspend, single, and halt. If set to ignore, the audit daemon does nothing. Syslog means that it will issue a warning to syslog. exec /path-to-script will execute the script. You cannot pass parameters to the script. Suspend will cause the audit daemon to stop writing records to the disk. The daemon will still be alive. The single option will cause the audit daemon to put the computer system in single user mode. halt option will cause the audit daemon to shutdown the computer system.

disk_error_action

This parameter tells the system what action to take whenever there is an error detected when writing audit events to disk or rotating logs. Valid values are ignore, syslog, exec, suspend, single, and halt. If set to ignore, the audit daemon does nothing. Syslog means that it will issue a warning to syslog. exec /path-to-script will execute the script. You cannot pass parameters to the script. Suspend will cause the audit daemon to stop writing records to the disk. The daemon will still be alive. The single option will cause the audit daemon to put the computer system in single user mode. halt option will cause the audit daemon to shutdown the computer system.

tcp_listen_port

This is a numeric value in the range 1..65535 which, if specified, causes auditd to listen on the corresponding TCP port for audit records from remote systems. The audit daemon may be linked with tcp_wrappers. You may want to controll access with an entry in the hosts.allow and deny files.

tcp_listen_queue

This is a numeric value which indicates how many pending (requested but unaccepted) connections are allowed. The default is 5. Setting this too small may cause connections to be rejected if too many hosts start up at exactly the same time, such as after a power failure.

tcp_max_per_addr

This is a numeric value which indicates how many concurrent connections from one IP address is allowed. The default is 1 and the maximum is 16. Setting this too large may allow for a Denial of Service attack on the logging server. The default should be adequate in most cases unless a custom written recovery script runs to forward unsent events. In this case you would increase the number only large enough to let it in too.

use_libwrap

This setting determines whether or not to use tcp_wrappers to discern connection attempts that are from allowed machines. Legal values are either yes, or no The default value is yes.

tcp_client_ports

This parameter may be a single numeric value or two values separated by a dash (no spaces allowed). It indicates which client ports are allowed for incoming connections. If not specified, any port is allowed. Allowed values are 1..65535. For example, to require the client use a priviledged port, specify 1-1023 for this parameter. You will also need to set the local_port option in the audisp-remote.conf file. Making sure that clients send from a privileged port is a security feature to prevent log injection attacks by untrusted users.

tcp_client_max_idle

This parameter indicates the number of seconds that a client may be idle (i.e. no data from them at all) before auditd complains. This is used to close inactive connections if the client machine has a problem where it cannot shutdown the connection cleanly. Note that this is a global setting, and must be higher than any individual client heartbeat_timeout setting, preferably by a factor of two. The default is zero, which disables this check.

enable_krb5

If set to "yes", Kerberos 5 will be used for authentication and encryption. The default is "no".

krb5_principal

This is the principal for this server. The default is "auditd". Given this default, the server will look for a key named like auditd/hostname@EXAMPLE.COM stored in /etc/audit/audit.key to authenticate itself, where hostname is the canonical name for the server's host, as returned by a DNS lookup of its IP address.

krb5_key_file

Location of the key for this client's principal. Note that the key file must be owned by root and mode 0400. The default is /etc/audit/audit.key

NOTES

In a CAPP environment, the audit trail is considered so important that access to system resources must be denied if an audit trail cannot be created. In this environment, it would be suggested that /var/log/audit be on its own partition. This is to ensure that space detection is accurate and that no other process comes along and consumes part of it.

The flush parameter should be set to sync or data.

Max_log_file and num_logs need to be adjusted so that you get complete use of your partition. It should be noted that the more files that have to be rotated, the longer it takes to get back to receiving audit events. Max_log_file_action should be set to keep_logs.

Space_left should be set to a number that gives the admin enough time to react to any alert message and perform some maintenance to free up disk space. This would typically involve running the aureport -t report and moving the oldest logs to an archive area. The value of space_left is site dependant since the rate at which events are generated varies with each deployment. The space_left_action is recommended to be set to email. If you need something like an snmp trap, you can use the exec option to send one.

Admin_space_left should be set to the amount of disk space on the audit partition needed for admin actions to be recorded. Admin_space_left_action would be set to single so that use of the machine is restricted to just the console.

The disk_full_action is triggered when no more room exists on the partition. All access should be terminated since no more audit capability exists. This can be set to either single or halt.

The disk_error_action should be set to syslog, single, or halt depending on your local policies regarding handling of hardware malfunctions.

Specifying a single allowed client port may make it difficult for the client to restart their audit subsystem, as it will be unable to recreate a connection with the same host addresses and ports until the connection closure TIME_WAIT state times out.

FILES

/etc/audit/auditd.conf

Audit daemon configuration file

SEE ALSO

auditd(8), audisp-remote.conf(5).

AUTHOR

Steve Grubb