Before you start Snapshoot your Droplet
Paste this (at the end of the file) to /etc/sysctl.conf (using nano /etc/sysctl.conf) and save it (this change not only fixes your error it makes your System much better),
### IMPROVE SYSTEM MEMORY MANAGEMENT ###
# Increase size of file handles and inode cache
fs.file-max = 2097152
# Do less swapping
vm.swappiness = 10
vm.dirty_ratio = 60
vm.dirty_background_ratio = 2
### GENERAL NETWORK SECURITY OPTIONS ###
# Number of times SYNACKs for passive TCP connection.
net.ipv4.tcp_synack_retries = 2
# Allowed local port range
net.ipv4.ip_local_port_range = 2000 65535
# Protect Against TCP Time-Wait
net.ipv4.tcp_rfc1337 = 1
# Decrease the time default value for tcp_fin_timeout connection
net.ipv4.tcp_fin_timeout = 15
# Decrease the time default value for connections to keep alive
net.ipv4.tcp_keepalive_time = 300
net.ipv4.tcp_keepalive_probes = 5
net.ipv4.tcp_keepalive_intvl = 15
### TUNING NETWORK PERFORMANCE ###
# Default Socket Receive Buffer
net.core.rmem_default = 31457280
# Maximum Socket Receive Buffer
net.core.rmem_max = 12582912
# Default Socket Send Buffer
net.core.wmem_default = 31457280
# Maximum Socket Send Buffer
net.core.wmem_max = 12582912
# Increase number of incoming connections
net.core.somaxconn = 65535
# Increase number of incoming connections backlog
net.core.netdev_max_backlog = 65535
# Increase the maximum amount of option memory buffers
net.core.optmem_max = 25165824
# Increase the maximum total buffer-space allocatable
# This is measured in units of pages (4096 bytes)
net.ipv4.tcp_mem = 65535 131072 262144
net.ipv4.udp_mem = 65535 131072 262144
# Increase the read-buffer space allocatable
net.ipv4.tcp_rmem = 8192 87380 16777216
net.ipv4.udp_rmem_min = 16384
# Increase the write-buffer-space allocatable
net.ipv4.tcp_wmem = 8192 65535 16777216
net.ipv4.udp_wmem_min = 16384
# Increase the tcp-time-wait buckets pool size to prevent simple DOS attacks
net.ipv4.tcp_max_tw_buckets = 1440000
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_tw_reuse = 1
Paste this (at the end of the file) to /etc/security/limits.conf (using nano /etc/security/limits.conf) and save it,
nginx soft nofile 2097152
nginx hard nofile 2097152
www-data soft nofile 2097152
www-data hard nofile 2097152
Paste this (at the end of the file) to /etc/pam.d/common-session (using nano /etc/pam.d/common-session) and save it,
session required pam_limits.so
Change listen.backlog in /etc/php5/fpm/pool.d/www.conf (using nano /etc/php5/fpm/pool.d/www.conf) and save it,
listen.backlog = 65535
Change workerrlimitnofile in /etc/nginx/nginx.conf (using nano /etc/nginx/nginx.conf) and save it,
worker_rlimit_nofile 99999;
And finally reboot 🙂