When Redis fails to start via systemctl on CentOS 7 despite manual execution working, we're typically dealing with either:

1. Systemd unit file misconfiguration
2. Resource limitations (file descriptors)
3. Permission/security context issues

The critical error message reveals the root cause:

[1972] 29 Jul 18:52:16.258 # Redis can't set maximum open files to 10032 because of OS error: Operation not permitted.
[1972] 29 Jul 18:52:16.258 # Current maximum open files is 1024.

This indicates Redis requires more file descriptors than the current user limit allows.

1. Adjusting System Limits

Create a dedicated limits configuration for Redis:

echo "redis soft nofile 10032" >> /etc/security/limits.conf
echo "redis hard nofile 10032" >> /etc/security/limits.conf

2. Modifying the Systemd Service File

Edit the Redis systemd unit to properly handle limits:

# Create override directory if it doesn't exist
mkdir -p /etc/systemd/system/redis-server.service.d/

# Create limit configuration
cat > /etc/systemd/system/redis-server.service.d/limits.conf << EOF
[Service]
LimitNOFILE=10032
EOF

3. Fixing the Overcommit Memory Warning

Address the memory configuration warning:

echo "vm.overcommit_memory = 1" >> /etc/sysctl.conf
sysctl -p

4. SELinux Context Considerations

If SELinux is enforcing, check and correct the context:

# Check SELinux status
sestatus

# If enforcing, correct context
semanage fcontext -a -t redis_var_lib_t '/var/lib/redis(/.*)?'
restorecon -Rv /var/lib/redis

After implementing all changes:

systemctl daemon-reload
systemctl restart redis-server
systemctl status redis-server

Check the journal for detailed errors if issues persist:

journalctl -xe -u redis-server

For memory-constrained environments (512MB VPS), consider adjusting Redis config:

# /etc/redis.conf
maxclients 4064
maxmemory 256mb
maxmemory-policy allkeys-lru

When attempting to start Redis via systemctl start redis-server on CentOS 7, many administrators encounter a puzzling situation where the command fails silently. The service appears to start briefly (as seen in systemctl status output) but immediately terminates.

The /var/log/redis/redis.log reveals two critical warnings:

[1972] 29 Jul 18:52:16.258 # Redis can't set maximum open files to 10032 because of OS error: Operation not permitted.
[1972] 29 Jul 18:52:16.258 # Current maximum open files is 1024. maxclients has been reduced to 4064
[1972] 29 Jul 18:52:16.259 # WARNING overcommit_memory is set to 0!

The primary issues stem from:

• Insufficient file descriptor limits (ulimit)
• Improper memory overcommit settings
• Systemd service unit configuration mismatch

Step 1: Permanently increase file descriptors

# Add to /etc/security/limits.conf
redis soft nofile 10032
redis hard nofile 10032

# Verify with:
su - redis -c 'ulimit -n'

Step 2: Configure memory overcommit

echo "vm.overcommit_memory = 1" >> /etc/sysctl.conf
sysctl -p

Step 3: Modify systemd service unit

# Create override file
mkdir -p /etc/systemd/system/redis-server.service.d
cat > /etc/systemd/system/redis-server.service.d/limits.conf <

systemctl start redis-server
systemctl status redis-server
redis-cli ping

PONG

maxclients 1000
maxmemory 256mb
maxmemory-policy allkeys-lru

journalctl -u redis-server -f
strace -f systemctl start redis-server
ls -l /var/run/redis.pid