Logs

Commands

View Recent Logs

Systemd Services:

journalctl -u $SERVICE -n 100 --no-pager
# Follow mode
journalctl -u $SERVICE -f

Docker Containers:

docker logs $CONTAINER --tail 100
# Follow mode
docker logs $CONTAINER -f

Application Log Files:

tail -n 100 ~/Projects/$PROJECT/logs/app.log
# Follow mode
tail -f ~/Projects/$PROJECT/logs/app.log

Filter by Level

Errors Only:

# Systemd
journalctl -u $SERVICE -p err -n 100 --no-pager

# Docker/Files
docker logs $CONTAINER 2>&1 | grep -i "error\|exception\|traceback"

# Log files
grep -i "error\|exception\|traceback" ~/Projects/$PROJECT/logs/app.log

Warnings:

grep -i "warn\|warning" $LOG_SOURCE

Search Logs

# Search for pattern
journalctl -u $SERVICE | grep -i "$PATTERN"
docker logs $CONTAINER 2>&1 | grep -i "$PATTERN"
grep -i "$PATTERN" ~/Projects/$PROJECT/logs/*.log

Time-Based Filtering

# Last hour
journalctl -u $SERVICE --since "1 hour ago"

# Today
journalctl -u $SERVICE --since today

# Specific time range
journalctl -u $SERVICE --since "2024-01-01 00:00:00" --until "2024-01-01 23:59:59"

Log Aggregation Mode

View logs from multiple services at once:

# All Erudition services
journalctl -u erudition-service -u mathmatters-service -f

# All Docker containers
docker-compose logs -f

Log Analysis

Count Errors by Type

grep -i "error" $LOG_FILE | sort | uniq -c | sort -rn | head -20

Find Slow Requests

grep -E "took [0-9]+ms" $LOG_FILE | awk '{print $NF}' | sort -rn | head -10

Track Request IDs

grep "$REQUEST_ID" $LOG_FILE

Output Format

Logs: [service-name]
Source: [systemd/docker/file]
Filter: [all/error/warn]
Time: [range]

---
[Formatted log entries with timestamps]
---

Summary:
- Total entries: X
- Errors: Y
- Warnings: Z
- Time span: [start] to [end]

Common Log Patterns

FastAPI (Python)

INFO:     127.0.0.1:52847 - "GET /health HTTP/1.1" 200 OK
ERROR:    Exception in route handler: [error message]

Next.js

ready - started server on 0.0.0.0:3000
error - Error: [error message]
warn - [warning message]

Docker

[timestamp] [level] [message]

Troubleshooting

If logs are empty:

1. Check if service is running: systemctl status $SERVICE
2. Check log rotation: ls -la /var/log/
3. Check Docker container status: docker ps -a
4. Verify log file permissions