Hosting Operations
Read-onlyCheck Whether PostgreSQL Is Accepting Connections
An app cannot reach PostgreSQL and you need a quick first-response check before digging into logs or credentials.
Command
pg_isready -h 127.0.0.1 -p 5432Before you run this
System impact: Read-only. Low when scoped to the shown target.
When not to use it: Do not treat readiness as proof that a specific user, database, or query works.
Expected output
A line showing host, port, and whether PostgreSQL is accepting connections.
System impact
Read-only. Nothing changes. pg_isready reports whether the server accepts connections.
Recovery / rollback: no state is changed.
When to use it
Use during deploys, incident triage, service restarts, and health checks.
When not to use it
Do not treat readiness as proof that a specific user, database, or query works.
next steps
Related commands
Check Whether MySQL Responds
The port was open. MySQL still had to answer.
mysqladmin ping -h 127.0.0.1 -P 3306
Show Active MySQL Sessions
The app was waiting behind busy sessions.
mysql -e "show full processlist;"
Check PostgreSQL Lock Waits
The outage was a queue, not a crash.
psql -X -c "select pid, wait_event_type, wait_event, state, left(query, 80) as query from pg_stat_activity where wait_event_type is not null order by pid;"
Show Active PostgreSQL Connections
The database was not down. It was full.
psql -X -A -F '|' -c "select pid,usename,datname,state,client_addr from pg_stat_activity order by state, pid;"
Find Long-Running PostgreSQL Queries
One query can make the whole app look broken.
psql -X -c "select pid, now() - query_start as age, state, left(query, 80) as query from pg_stat_activity where query_start is not null order by age desc limit 10;"
Study mapping
Use this as independent command practice: read the notes, predict the output, then compare it with the example before using a real shell.
Independent study support only. No affiliation, endorsement, exam dumps, or real exam questions.