Log management and rotation in Jenkins - Step-by-Step Execution

Process Flow - Log management and rotation

Jenkins generates logs

↓

Log file grows

↓

Check log size or age

↓

Rotate logs

↓

Archive old logs

↓

Delete logs older than retention

↓

New log file created

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Repeat cycle

Jenkins writes logs continuously. When logs get too big or old, Jenkins rotates them by archiving and starting fresh logs, then deletes old archives based on retention.

Execution Sample

Jenkins

pipeline {
  agent any
  options {
    buildDiscarder(logRotator(numToKeepStr: '3'))
  }
  stages {
    stage('Example') { steps { echo 'Hello' } }
  }
}

This Jenkins pipeline configures log rotation to keep only the last 3 builds' logs.

Process Table

Step	Action	Log Size or Age Check	Rotation Triggered	Result
1	Build #1 runs	Log size < limit	No	Log appended, no rotation
2	Build #2 runs	Log size < limit	No	Log appended, no rotation
3	Build #3 runs	Log size < limit	No	Log appended, no rotation
4	Build #4 runs	Log size > limit	Yes	Old logs archived, oldest deleted, new log file created
5	Build #5 runs	Log size < limit	No	Log appended, no rotation

💡 Rotation stops when logs are within size limits and retention count is maintained

Status Tracker

Variable	Start	After Build #1	After Build #2	After Build #3	After Build #4	After Build #5
Log Size	0KB	50KB	100KB	150KB	50KB (rotated)	100KB
Archived Logs Count	0	0	0	0	1	1
Current Log File	log-0.txt	log-0.txt	log-0.txt	log-0.txt	log-1.txt	log-1.txt

Key Moments - 3 Insights

Why does the log size drop after Build #4?

Because at Build #4, log rotation happens (see execution_table row 4), old logs are archived and a new log file starts fresh, reducing current log size.

What triggers the log rotation?

The log rotation triggers when the log size exceeds the configured limit or the number of builds exceeds retention (execution_table row 4).

Why are some old logs deleted after rotation?

To keep only a set number of archived logs as per retention policy, oldest logs are deleted to save space (see variable_tracker Archived Logs Count).

Visual Quiz - 3 Questions

Look at the execution table, what is the log size after Build #3?

A 100KB

B 150KB

C 50KB

D 0KB

💡 Hint

Check the 'Log Size' column in variable_tracker after Build #3

At which build does log rotation occur?

A Build #2

B Build #3

C Build #4

D Build #5

💡 Hint

See execution_table row where 'Rotation Triggered' is Yes

If retention is set to keep 5 builds instead of 3, what changes in the execution table?

A Rotation triggers later, after Build #6

B Rotation triggers earlier, after Build #2

C Rotation never triggers

D Rotation triggers at Build #4 as before

💡 Hint

Retention controls when rotation triggers based on number of builds kept

Concept Snapshot

Jenkins log rotation keeps logs manageable.
Configure with buildDiscarder(logRotator).
Set number of builds or days to keep.
When logs exceed limits, Jenkins archives old logs.
Oldest logs deleted to save space.
New log files start fresh after rotation.

Full Transcript

Jenkins creates logs for each build. As logs grow, Jenkins checks if they exceed size or age limits. If yes, Jenkins rotates logs by archiving old ones and deleting the oldest beyond retention. This keeps logs from using too much space. The pipeline example uses buildDiscarder with logRotator to keep only the last 3 builds' logs. The execution table shows builds 1 to 5, with rotation happening at build 4 when logs exceed size. Variables track log size, archived logs count, and current log file name. Key moments clarify why log size drops after rotation and what triggers rotation. The quiz tests understanding of log size, rotation timing, and retention effects.