pickup Daemon in Linux
The pickup in Linux is a Postfix daemon responsible for detecting new mail in the maildrop directory and passing it to the cleanup daemon. Malformed files are deleted without notification. It is designed to run under the control of the master process manager and operates with low privileges, enhancing security by minimizing potential risks associated with reading files from untrusted sources.
Table of Contents
Here is a comprehensive guide to the options available with the pickup command â
- Syntax of pickup Daemon
- pickup Daemon Options
- Configuration for pickup Daemon
- Checking the Status of pickup Daemon
- Modifying Configurations for pickup Daemon
- Post Configuration Process
Syntax of pickup Daemon
The syntax of the pickup daemon is as follows −
pickup [generic Postfix daemon options]
The pickup daemon can be configured with several generic options mentioned in the next section that control its behavior.
pickup Daemon Options
The generic options of the pickup daemon are listed below −
| Option | Description |
|---|---|
| content_filter | After the message is queued, send the entire message to the specified transport:destination. |
| receive_override_options | Enable or disable recipient validation, built-in content filtering, or address mapping. |
| config_directory | The default location of the Postfix main.cf and master.cf configuration files. |
| ipc_timeout | The time limit for sending or receiving information over an internal communication channel. Default: 3600s. |
| line_length_limit | Upon input, long lines are chopped up into pieces of at most this length; upon delivery, long lines are reconstructed. Default: 2048. |
| max_idle | The maximum amount of time that an idle Postfix daemon process waits for an incoming connection before terminating voluntarily. Default: 100s. |
| max_use | The maximal number of incoming connections that a Postfix daemon process will service before terminating voluntarily. Default: 100. |
| process_id | The process ID of a Postfix command or daemon process. (Read-only) |
| process_name | The process name of a Postfix command or daemon process. (Read-only) |
| queue_directory | The location of the Postfix top-level queue directory. |
| syslog_facility | The syslog facility of Postfix logging. Default: mail. |
| syslog_name | A prefix that is prepended to the process name in syslog records, so that, for example, smtpd becomes prefix/smtpd. |
| service_name | The master.cf service name of a Postfix daemon process. (Available in Postfix 3.3 and later.) |
| info_log_address_format | The email address form that will be used in non-debug logging (info, warning, etc.). (Available in Postfix 3.5 and later) |
Checking the Status of pickup Daemon
To check the status of the pickup service, use the following command −
ps aux | grep pickup
The output shows the pickup process is running as a Postfix daemon.
Configuration of pickup Daemon
Postfix automatically manages the pickup daemon and does not require direct configuration. However, its behavior can be adjusted using Postfix configuration files (main.cf and master.cf). Below are key configuration steps and examples −
The pickup service is defined in /etc/postfix/master.cf. Ensure this entry exists and is not commented out −
sudo nano /etc/postfix/master.cf
- Service name:Â pickup
- Communication method:Â Unix domain socket (unix)
- Chrooted:Â No chroot environment (n)
- Per-user privilege:Â Not used (-)
- Log to syslog:Â Yes (y)
- Idle timeout:Â 60 seconds before terminating (60)
- Max concurrent processes:Â 1 (1)
- Command: Runs the pickup process itself (pickup)
The above options can be modified to change the pickup service definition. Other parameters that can be specified in the master file are listed below −
Setting max_use
To set the maximum number of incoming connections that a pickup process will service before terminating, modify the max_use parameter. By default, this is 100.
max_use = 200
Setting max_idle
To set the maximum idle time before the pickup process terminates, set the max_idle parameter.
max_idle = 300s
The default idle time for the pickup daemon is 100s.
To apply the changes, restart the Postfix service.
Modifying Configurations for pickup Daemon
In this section, various options for pickup daemon will be discussed along with the process to set them.
The pickup service options are configured in /etc/postfix/main.cf file. To access this file, use any text editor with sudo privileges.
sudo nano /etc/postfix/main.cf
Setting ipc_timeout
The ipc_timeout defines the time limit for sending or receiving data over an internal communication channel. By default, it is 3600 seconds, however, it can be added or modified.
ipc_timeout = 7200
Setting line_length_limit
The line_length_limit controls the maximum length of lines Postfix will accept. By default, this is 2048.
line_length_limit = 3000
Setting config_directory
To check the default, configuration directory, use the following command −
postconf -d | grep config_directory
By default, it is /etc/postfix. It can be changed by specifying the config_directory in the main.cf file.
config_directory = /path/to/directory
Post Configuration Process
After making the modifications in the main.cf or master.cf file, restart the Postfix to apply the changes.
sudo systemctl restart postfix
Conclusion
The pickup daemon plays a crucial role in handling new mail by detecting files in the maildrop directory and passing them to the cleanup daemon. It operates with minimal privileges to enhance security, ensuring the safe handling of untrusted files.
Although it doesn't require direct configuration, various options like ipc_timeout, line_length_limit, and max_idle can be adjusted through configuration files such as main.cf and master.cf. After modifying these settings, restarting Postfix ensures that changes take effect.