postgresql can not start after change the data_directory - postgresql

Question

I use postgresql on Debian.
The postgresql service can not start after I edit the config file:
#data_directory = '/var/lib/postgresql/9.4/main' # use data in another directory
data_directory = '/opt/data/postgresql/data'
(yeah,I just use custom directory instead of the default data_directory)
I find the log in /var/log/syslog
Sep 14 10:22:17 thinkserver-ckd postgresql#9.4-main[11324]: Error: could not exec /usr/lib/postgresql/9.4/bin/pg_ctl /usr/lib/postgresql/9.4/bin/pg_ctl start -D /opt/data/postgresql/data -l /var/log/postgresql/postgresql-9.4-main.log -s -o -c config_file="/etc/postgresql/9.4/main/postgresql.conf" :
Sep 14 10:22:17 thinkserver-ckd systemd[1]: postgresql#9.4-main.service: control process exited, code=exited status=1
Sep 14 10:22:17 thinkserver-ckd systemd[1]: Failed to start PostgreSQL Cluster 9.4-main.
Sep 14 10:22:17 thinkserver-ckd systemd[1]: Unit postgresql#9.4-main.service entered failed state.
And nothing in /var/log/postgresql/postgresql-9.4-main.log
Thanks.
I finally got this answer:
What this error means in PostgreSQL?
#langton 's answer.
He said that
you should run pg_upgradecluster or similar, or just create a new cluster with pg_createcluster (these commands are for debian systems - you didn't specify your OS)
So I executed the command:
pg_createcluster -d /opt/data/postgresql/data -l /opt/data/postgresql/log 9.4 ckd
And then :
service postgresql restart
it started!

Answer 1

If downtime is allowed and you already have databases with data in the old cluster location you only need to physically copy the data to the new location.
This is a more or less common operation if you partition is out of space.
# Check that current data directory is the same that
# the one in the postgresql.conf config file
OLD_DATA_DIR=$(sudo -u postgres psql --no-psqlrc --no-align --tuples-only --quiet -c "SHOW data_directory;")
echo "${OLD_DATA_DIR}"
CONFIG_FILE=$(sudo -u postgres psql --no-psqlrc --no-align --tuples-only --quiet -c "SHOW config_file;")
echo "${CONFIG_FILE}"
# Stop PostgreSLQ
systemctl stop postgresql
# Change the data directory in the config
# Better to do it with an editor, instead of sed
NEW_DATA_DIR='/opt/data/postgresql/data'
sed -i "s%data_directory = '${OLD_DATA_DIR}'%data_directory = '${NEW_DATA_DIR}'%" "${CONFIG_FILE}"
# Move/Copy the data for example using rsync
rsync -av --dry-run "${OLD_DATA_DIR}" "${NEW_DATA_DIR}"
# Take care with the classical issues of rsync and end backslashes
rsync -av "${OLD_DATA_DIR}" "${NEW_DATA_DIR}"
# Rename the old dir, just to avoid missunderstandings and set
# check the permissions on the new one
# Start postgres
systemctl start postgresql
# Check that everything goes well and eventually drop the old data
# Make sure that the logs and everything else is where you want.