log_file_mode

log_file_mode is the PostgreSQL setting that defines the file permissions for log files.

Note

Fact — official short description: “Sets the file permissions for log files.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valuesighup: Takes effect after configuration reload
Unit , Value—: Raw unit
Range , Value0 – 511: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueReporting and Logging / Where to Log: Upstream classification
Latest boot value , Value384: 384

Lifecycle

Fact	Value
First observed	PG9.1
Present in	PG9.1–19 Beta 3
Removed in	No
Introduction commit	`3ec694e17bc0` — Add a log_file_mode GUC that allows control of the file permissions set on log files created by the syslogger process.
Commit date	2010-07-16
Discussion	—

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG9.1–19 Beta 3	`384`	—	384

How it works

log_file_mode is a chmod-style numeric mode for files newly created by logging_collector. Use a leading zero for customary octal notation: 0640 is not the same numeric value as decimal 640. The setting does not apply to syslog/eventlog output and does not change existing files.

It has SIGHUP context. After a reload, the new mode is used the next time logging_collector creates a file; reloading does not chmod the file that is currently open or historical files.

The effective access boundary also includes the PostgreSQL service account, file group, log_directory ownership and traversal permissions, shipping-agent group membership, and external retention copies. A group-readable mode is safe only when that group is controlled.

Tuning advice

Tip

Advice. These are workload-specific starting points and must be validated with measurements.

Workload	Guidance
OLTP	Choose the least-privileged mode that still lets the approved collector or shipping group read new files. Verify ownership after a real rotation and explicitly remediate existing files if policy changes.
OLAP	Analytical logs often contain query text and identifiers, so use the same or stricter mode; larger log volume is not a reason to broaden file access.
Small nodes	Keep 0600 unless a controlled local group must ship logs; if 0640 is used, audit group membership and directory permissions rather than making files world-readable.

Pigsty

Values use the fixed 8-vCPU, 32-GiB, 100-GiB SSD fixture and render the current Pigsty templates for PG19 Beta 3; this does not assert current Pigsty support for that historical or beta release.

Template	Effective value	Versus upstream boot	Source expression
OLTP	`0640`	different	`'0640'`
OLAP	`0640`	different	`'0640'`
CRIT	`0640`	different	`'0640'`
TINY	`0640`	different	`'0640'`

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.1–19 Beta 3 = 0640 (dcs); OLAP: PG9.1–19 Beta 3 = 0640 (dcs); CRIT: PG9.1–19 Beta 3 = 0640 (dcs); TINY: PG9.1–19 Beta 3 = 0640 (dcs). Advice, pending human review — Editorial inference: 0640 keeps log files private from other users while allowing an operational group to read and ship them.

Common pitfalls

Editing log_file_mode without reloading configuration and verifying the effective value and subsequent behavior.
Combining incompatible destination, collector, filename, and rotation assumptions and then losing or overwriting logs.
Failing to monitor a full or unwritable log target, which can block logging or database activity depending on the path.
Writing 640 instead of octal 0640 and producing a different numeric permission mode.

logging_collector · log_destination · log_directory · log_filename · log_rotation_age · log_rotation_size