FLUSH(8)

🦋 FLUSH(8) 🦋

okay bestie, we are deep in the System Manager's Manual and this page is literally FLUSH(8). grab a boba, this one's short and honestly kind of iconic.

---

✨ NAME ✨

flush — Postfix fast flush server 💖

🎀 SYNOPSIS 🎀

flush [generic Postfix daemon options]

💅 DESCRIPTION 💅

okay so the flush(8) server is out here keeping a whole record of your deferred mail by destination, bestie. why? because it makes the SMTP ETRN request go brrr, and same for its command-line equivalents, sendmail -qR and postqueue -f. this program expects to be launched from the master(8) process manager, so don't just run it yourself like a menace. 🫶

the record is a per-destination logfile, and its contents are the queue IDs of deferred mail. a logfile is append-only, and it gets truncated when delivery is requested for that destination. and a "destination"? it's the part on the right-hand side of the right-most @ in an email address. iykyk. ✨

per-destination logfiles of deferred mail are only maintained for eligible destinations. the list of eligible destinations is set with the fast_flush_domains configuration parameter, which defaults to $relay_domains. slay.

this server implements the following requests:

• add sitename queueid — tell the flush(8) server that the message with the specified queue ID is queued up for the specified destination. 💌
• send_site sitename — request delivery of mail that's queued for the specified destination. go go go 🚀
• send_file queueid — request delivery of the specified deferred message. one specific little guy. 🎀
• refresh — refresh non-empty per-destination logfiles that were not read in $fast_flush_refresh_time hours, by simulating send requests (see above, bestie) for the corresponding destinations. it also deletes empty per-destination logfiles that were not updated in $fast_flush_purge_time days. this request completes in the background, so it's lowkey doing its own thing. 🧚
• purge — do a refresh for all per-destination logfiles. no cap.

🔒 SECURITY 🔒

the flush(8) server is not security-sensitive. it does not talk to the network, and it does not talk to local users. it's literally just vibing internally. the fast flush server can run chrooted at fixed low privilege. 👑

🩺 DIAGNOSTICS 🩺

problems and transactions get logged to syslogd(8) or postlogd(8). so if something's weird, check there first, bestie.

💀 BUGS 💀

okay this part is giving "read the fine print":

• Fast flush logfiles are truncated only after a send request, NOT when mail is actually delivered. so yeah, they can accumulate outdated or redundant data. 😭
• to maintain sanity, refresh must be executed periodically. this can be automated with a suitable wakeup timer setting in the master.cf configuration file. set it and forget it. ⏰
• upon receipt of a request to deliver mail for an eligible destination, the flush(8) server requests delivery of all messages listed in that destination's logfile, regardless of the recipients of those messages. this is not an issue for mail sent to a relay_domains destination, because such mail typically only has recipients in one domain. 🙈

⚙️ CONFIGURATION PARAMETERS ⚙️

changes to main.cf are picked up automatically, because flush(8) processes only run for a limited amount of time. use the command postfix reload to speed up a change. ✨

the text below provides only a parameter summary. see postconf(5) for more details, including examples. 💜

• config_directory (see 'postconf -d' output) — the default location of the Postfix main.cf and master.cf configuration files.
• daemon_timeout (18000s) — how much time a Postfix daemon process may take to handle a request before it is terminated by a built-in watchdog timer. ⏳
• fast_flush_domains ($relay_domains) — optional list of destinations that are eligible for per-destination logfiles with mail that is queued to those destinations.
• fast_flush_refresh_time (12h) — the time after which a non-empty but unread per-destination "fast flush" logfile needs to be refreshed.
• fast_flush_purge_time (7d) — the time after which an empty per-destination "fast flush" logfile is deleted.
• ipc_timeout (3600s) — the time limit for sending or receiving information over an internal communication channel.
• max_idle (100s) — the maximum amount of time that an idle Postfix daemon process waits for an incoming connection before terminating voluntarily.
• max_use (100) — the maximal number of incoming connections that a Postfix daemon process will service before terminating voluntarily.
• parent_domain_matches_subdomains (see 'postconf -d' output) — a list of Postfix features where the pattern example.com also matches subdomains of example.com, instead of requiring an explicit .example.com pattern.
• process_id (read-only) — the process ID of a Postfix command or daemon process.
• process_name (read-only) — the process name of a Postfix command or daemon process.
• queue_directory (see 'postconf -d' output) — the location of the Postfix top-level queue directory.
• syslog_facility (mail) — the syslog facility of Postfix logging.
• syslog_name (see 'postconf -d' output) — a prefix that is prepended to the process name in syslog records, so that, for example, smtpd becomes prefix/smtpd.

available in Postfix 3.3 and later:

• service_name (read-only) — the master.cf service name of a Postfix daemon process. 🆕

📁 FILES 📁

• /var/spool/postfix/flush, "fast flush" logfiles. 🗂️

👀 SEE ALSO 👀

• smtpd(8), SMTP server
• qmgr(8), queue manager
• postconf(5), configuration parameters
• master(5), generic daemon options
• master(8), process manager
• postlogd(8), Postfix logging
• syslogd(8), system logging

📖 README FILES 📖

use postconf readme_directory or postconf html_directory to locate this information, bestie.

• ETRN_README, Postfix ETRN howto 🌈

📜 LICENSE 📜

the Secure Mailer license must be distributed with this software. periodt. ✋

🕰️ HISTORY 🕰️

this service was introduced with Postfix version 1.0. an og. 👑

👩‍💻 AUTHOR(S) 👩‍💻

• Wietse Venema IBM T.J. Watson Research P.O. Box 704 Yorktown Heights, NY 10598, USA
• Wietse Venema Google, Inc. 111 8th Avenue New York, NY 10011, USA

---

and that's the whole FLUSH(8) page from the System Manager's Manual, bestie — go forth and fast-flush responsibly. 💖✨🎀