19.2.5.4 Exec Admin Command

Administrative commands executed via docker exec allow operators to perform maintenance, configuration, and management operations inside a running container without stopping it, modifying the image, or creating a new container. These operations range from database administration to process management, configuration reloading, user management, and service health checks — all carried out within the live container environment.

Running as Root for Admin Operations

Many administrative operations require root privileges. If the container's primary process runs as a non-root user, the -u root flag grants root access for the exec'd command only:

docker exec -u root my-container bash

Or for a single command:

docker exec -u root my-container chown -R appuser:appgroup /data

The container continues running as its normal user after the admin command exits.

Database Administration

PostgreSQL

# Connect to the database interactively
docker exec -it postgres-container psql -U postgres

# Run a specific SQL command
docker exec postgres-container psql -U postgres -d mydb -c "VACUUM ANALYZE;"

# Create a database backup
docker exec postgres-container pg_dump -U postgres mydb > backup.sql

# Check database size
docker exec postgres-container psql -U postgres -c "\l+"

# Reload configuration without restart
docker exec postgres-container psql -U postgres -c "SELECT pg_reload_conf();"

MySQL/MariaDB

# Connect interactively
docker exec -it mysql-container mysql -u root -pSECRET

# Run a query
docker exec mysql-container mysql -u root -pSECRET mydb -e "SHOW TABLE STATUS;"

# Create a backup
docker exec mysql-container mysqldump -u root -pSECRET mydb > backup.sql

Redis

# Connect to Redis CLI
docker exec -it redis-container redis-cli

# Run a single command
docker exec redis-container redis-cli DBSIZE
docker exec redis-container redis-cli FLUSHDB

# Check memory usage
docker exec redis-container redis-cli INFO memory

MongoDB

# Connect interactively
docker exec -it mongo-container mongosh

# Run a single operation
docker exec mongo-container mongosh mydb --eval "db.users.countDocuments()"

Configuration Reload

Reloading a service's configuration file without restarting the container avoids downtime:

nginx

# Test configuration validity
docker exec nginx-container nginx -t

# Reload configuration (gracefully rotates workers)
docker exec nginx-container nginx -s reload

Signal-based reload

Many services reload their configuration when they receive SIGHUP. This can be triggered via docker kill --signal SIGHUP or from inside a shell session:

docker exec my-container sh -c "kill -HUP 1"

File and Permission Management

# Change ownership of a directory
docker exec -u root my-container chown -R 1001:1001 /data/uploads

# Change permissions
docker exec -u root my-container chmod 755 /app/scripts/start.sh

# Create a directory
docker exec my-container mkdir -p /app/cache/sessions

# Remove a lock file left by a crashed process
docker exec -u root my-container rm -f /tmp/app.lock

Log Rotation and Maintenance

# Truncate an application log file that has grown too large
docker exec -u root my-container truncate -s 0 /app/logs/debug.log

# Compress old log files
docker exec -u root my-container sh -c "gzip /app/logs/*.log.1"

# Remove logs older than 7 days
docker exec my-container find /app/logs -name "*.log" -mtime +7 -delete

User and Group Management

# Create a new user inside the container
docker exec -u root my-container adduser --disabled-password --gecos "" newuser

# Add a user to a group
docker exec -u root my-container usermod -aG docker newuser

Running Database Migrations

Many deployment workflows run migrations from inside the application container:

docker exec my-app-container ./manage.py migrate            # Django
docker exec my-app-container node migrate.js up             # Node.js
docker exec my-app-container rails db:migrate               # Rails
docker exec my-app-container php artisan migrate            # Laravel

Application Cache Clearing

docker exec my-app-container php artisan cache:clear
docker exec my-app-container rails runner "Rails.cache.clear"
docker exec my-app-container python3 manage.py clearcache

Health Verification

# Check the application responds correctly
docker exec my-container curl -s http://localhost:8080/health

# Check application version
docker exec my-container cat /app/VERSION

# Verify a service is listening on the expected port
docker exec my-container sh -c "ss -tlnp | grep 8080"

Service Process Management Inside the Container

Some containers run multiple processes managed by a supervisor. Administrative commands can manage these:

# With supervisord
docker exec my-container supervisorctl status
docker exec my-container supervisorctl restart worker

# With s6 overlay
docker exec my-container s6-svstat /var/run/s6/services/myapp

Scripted Administrative Workflows

For repeatable administrative operations:

#!/bin/bash
CONTAINER="my-database"

echo "Running maintenance on $CONTAINER..."
docker exec $CONTAINER psql -U postgres -c "VACUUM FULL ANALYZE;" -d mydb
docker exec $CONTAINER psql -U postgres -c "REINDEX DATABASE mydb;" -d mydb
echo "Maintenance complete."

This script can be scheduled as a cron job to run regular database maintenance against the running container without any downtime.