Set this in /etc/sysctl.conf net.ipv6.conf.all.disable_ipv6 = 1 #apply the settings sudo sysctl -p ........

systemd is like the service manager for your Centos and other modern Linux distributions (including Debian/Mint/Ubuntu) allows you to enable services, stop them, restart them, check their status and even reboot your system. The key commands or arguments you will use with systemctl are the following: Unit Commands: list-units [PATTERN...] List loaded units &nbs........

sudo apt-get install libcurl4-openssl-dev git build-essential autotools-dev autoconf libcurl3 sudo apt-get install libcurl4-gnutls-dev git clone https://github.com/wolf9466/cpuminer-multi sudo apt-get install cmake libpthread-* libmicrohttpd-dev libssl-dev libhwloc-dev git clone https://github.com/fireice-uk/xmr-stak-cpu.git make install cd bin chmod +x xmr-stak-cpu ./xmr-stak -O xmr........

PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib64/php/modules/geoip.so' - /usr/lib64/php/modules/geoip.so: undefined symbol: GeoIP_country_code_by_name_v6 in Unknown on line 0 Remove the GEOIP from PHP: php71w-pecl-geoip-1.1.1-1.w6.x86_64 PHP Fatal error: PHP Startup: apc_shm_create: shmget(0, 67108864, 914) failed: Invalid argument. It is possible that the........

The Linux Kernel interpretated a very high volume of real traffic as a DDOS attack so it basically ends up blocking your web server. possible SYN flooding on ctid 42131, port 80. Sending cookies. Simple fix edit sysctl values for max_syn_backlog sysctl -w net.ipv4.tcp_max_syn_backlog=5000 To make them permanent edit /etc/sysctl.conf echo "net.ipv4.tcp_........

PHP Fatal error: PHP Startup: apc_shm_create: shmget(0, 67108864, 914) failed: Invalid argument. It is possible that the chosen SHM segment size is higher than the operation system allows. Linux has usually a default limit of 32MB per segment. in Unknown on line 0 PHP Fatal error: PHP Startup: apc_shm_attach: shmat failed: in Unknown on line 0 This error is not at all fun because it actually prevents Apache/httpd from starting or working at all. It will........

iptables -t nat -A OUTPUT -m addrtype --src-type LOCAL --dst-type LOCAL -p tcp --dport 3306 -j DNAT --to-destination ip.ip.ip.ip iptables -t nat -A POSTROUTING -m addrtype --src-type LOCAL --dst-type UNICAST -j MASQUERADE sysctl -w net.ipv4.conf.all.route_localnet=1 Make sure you substitute "ip.ip.ip.ip" for your real public IP and also the "--dport 3306" for the port you want to forward. Finally run the sysctl command and........

Tired of checking iotop and seeing that your drbd partition is using 99.99% of io all the time and finding your drbd device performs slow in general? This is especially an issue in versions of DRBD in the 8.3 tree in particular one documented case is on "8.3.13" but it likely applies to other devices. The symptoms are that resyncing is fine and normal but any reasonable amount of activity is very slow and lagged and creates a high server load and con........

kernel: [10186978.064405] TCP: time wait bucket table overflow (CT3) Varying opinions are out there but in general it seems like the most common culprit is a lack of privvmpages, with a modern OpenVZ system the best way is to set privvmpages as equal to what your RAM is and this has resolved the messages on another system. If it's truly a TCP issue you can adjust the following parameters:........

yum -y install wget wget -P /etc/yum.repos.d/ http://ftp.openvz.org/openvz.repo rpm --import http://ftp.openvz.org/RPM-GPG-Key-OpenVZ yum -y install vzkernel vzctl #enable ip_forward sed -i s/'net.ipv4.ip_forward = 0'/'net.ipv4.ip_forward = 1'/g /etc/sysctl.conf #all interfaces should not send redirects echo "net.ipv4.conf.default.send_redirects = 1" >> /etc/sysctl.conf echo "net.ipv4.co........

yum -y install wget wget -P /etc/yum.repos.d/ http://ftp.openvz.org/openvz.repo rpm --import http://ftp.openvz.org/RPM-GPG-Key-OpenVZ yum -y install vzkernel vzctl After that just reboot and you may also have to enable ip_forward in /etc/sysctl.conf........

If you make changes to /etc/sysctl.conf (which are permanent and not lost during reboot) but want them to apply with rebooting just use the following command: sysctl -p After that your changes will be enabled.........

ip_conntrack: table full, dropping packet. A lot of clients I've seen have this issue, it really seems the default level is way too small. Once this connection tracking table becomes full then packets get dropped which is obviously a bad thing. One thing to be mindful of though is that 350 bytes of memory are used per entry so there is some justification for not keeping it too high. However, if you have multiple servers running or high traffic daemons........

ping test.com connect: No buffer space available /var/log/messages Oct 18 12:21:03 vps kernel: printk: 177 messages suppressed. Oct 18 12:21:03 vps kernel: Neighbour table overflow. Solution in /etc/sysctl.conf: net.ipv4.neigh.default.gc_thresh1 = 4096 net.ipv4.neigh.default.gc_thresh2 = 8192 net.ipv4.neigh.default.gc_thresh3 = 8192 net.ipv4.neigh.default.base_reachab........

service vz start Starting OpenVZ: failed to load module vzmon [FAILED] vzmon: Unknown symbol ve_snmp_proc_init vzmon: Unknown symbol addrconf_sysctl_free vzmon: Unknown symbol ve_ndisc_init vzmon: Unknown symbol addrconf_ifdown vzmon: Unknown symbol ip6_frag_cleanup vzmon: Unknown symbol fini_ve_route6........

service vz start Starting OpenVZ: failed to load module vzmon [FAILED] vzmon: Unknown symbol ve_snmp_proc_init vzmon: Unknown symbol addrconf_sysctl_free vzmon: Unknown symbol ve_ndisc_init vzmon: Unknown symbol addrconf_ifdown vzmon: Unknown symbol ip6_frag_cleanup vzmon: Unknown symbol fini_ve_route6 ........

cd /etc/yum.repos.d wget http://download.openvz.org/openvz.repo rpm --import http://download.openvz.org/RPM-GPG-Key-OpenVZ yum install ovz-kernel-PAE Now remember to set /etc/sysctl.conf to "net.ipv4.ip_forward = 1" You can apply the change immediately by running sysctl -w net.ipv4.ip_forward = 1 but remember that you still have to set sysctl.conf sysctl -p will load and apply any changes to s........

Problems surfing web/servingI noticed sometimes websites wouldn't load at random through a FreeBSD box and other systems on the same link didn't have the issue. I believe it is because of the low default limit of 128 TCP connections that caused the problem. It would also slow down any traffic that requires many connections such as Bittorrent. The fix is to increase the amount of connections to at least 1024 Edit [b:520b050d3e]/etc/sysctl.conf[/b:520b05........