MISCONF Redis is configured to save RDB snapshots, but it's currently unable to persist to disk. — how to fix

(error) MISCONF Redis is configured to save RDB snapshots, but it's currently unable to persist to disk. Commands that may modify the data set are disabled, because this instance is configured to report errors during writes if RDB snapshotting fails (stop-writes-on-bgsave-error option). Please check the Redis logs for details about the RDB error.

Quick fix: Check the log (journalctl -u redis-server or docker logs <container>) and redis-cli INFO persistence. Free disk space, fix ownership of the data dir (CONFIG GET dir; sudo chown redis:redis /var/lib/redis), or for fork errors set vm.overcommit_memory = 1. Then redis-cli BGSAVE to confirm. CONFIG SET stop-writes-on-bgsave-error no only hides the problem.

What it means

With RDB persistence on (the default save rules), Redis periodically forks a child that writes the dataset to dump.rdb. If the last save failed and stop-writes-on-bgsave-error is yes (the default), Redis rejects every write command with MISCONF until a save succeeds. Reads still work.

Find out why the save failed:

redis-cli INFO persistence | grep -E "rdb_last_bgsave_status|rdb_changes_since_last_save"
redis-cli CONFIG GET dir
redis-cli CONFIG GET dbfilename

sudo journalctl -u redis-server -n 50     # Debian/Ubuntu service name
sudo tail -n 50 /var/log/redis/redis-server.log
docker logs my-redis --tail 50            # in Docker

The log line that matters looks like Failed opening the temp RDB file temp-1234.rdb (in server root dir /var/lib/redis) for saving: Permission denied or Can't save in background: fork: Cannot allocate memory.

Cause 1: disk full

df -h "$(redis-cli CONFIG GET dir | tail -1)"

Free up space (old logs, Docker images, large files) or move the data directory to a bigger disk. Redis needs room for a full temporary copy of the RDB file while saving.

Cause 2: Redis can't write to its directory (Permission denied)

The data dir must be writable by the user Redis runs as:

sudo chown -R redis:redis /var/lib/redis
sudo chmod 750 /var/lib/redis

A frequent variant: the dir was changed at runtime to something like /etc or /root, sometimes by an attacker on an exposed Redis (CONFIG SET dir, CONFIG SET dbfilename). If CONFIG GET dir shows an odd location you didn't set, treat the server as compromised: make sure Redis isn't reachable from the internet (bind 127.0.0.1, protected-mode yes, a password via requirepass or ACLs, a firewall) and check for unexpected authorized_keys or cron entries. Then set the directory back:

redis-cli CONFIG SET dir /var/lib/redis
redis-cli CONFIG SET dbfilename dump.rdb

In Docker, make sure the mounted volume for /data is writable by the container's redis user.

Cause 3: fork fails (Cannot allocate memory)

Forking a large Redis process requires the kernel to allow overcommit. Redis itself warns about this at startup:

echo "vm.overcommit_memory = 1" | sudo tee /etc/sysctl.d/99-redis.conf
sudo sysctl --system

Also check that the server isn't genuinely out of RAM (free -m), and set maxmemory so Redis leaves headroom for the fork.

Confirm the fix

redis-cli BGSAVE
redis-cli INFO persistence | grep rdb_last_bgsave_status   # should be ok

Once a save succeeds, writes are accepted again.

If you don't need persistence

For a pure cache, turn off RDB snapshots instead of ignoring errors:

redis-cli CONFIG SET save ""
redis-cli CONFIG REWRITE      # persist to redis.conf

or save "" in redis.conf.

CONFIG SET stop-writes-on-bgsave-error no makes the error go away while saves keep failing silently; you'll lose data on restart without knowing it. Use it only as a temporary measure while you fix the real cause.

Last updated 2026-11-01.