sysctl vm.overcommit_memory=1 echo never > /sys/kernel/mm/transparent_hugepage/enabled echo 511 > /proc/sys/net/core/somaxconn 1:M 26 Nov 2023 21:34:33.840 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128. 1:M 26 Nov 2023 21:34:33.840 # Server initialized 1:M 26 Nov 2023 21:34:33.840 # WARNING overcommit_memory is set to 0! Background sa........

We could always disable swap but this would normally be a bad idea unless you have an incredible amount of RAM and a workload that will never exceed it. However, for live/containerized and high performance environments it could be desirable. Another middle ground may be to set swappiness to a lower number. You may also want to clear your kernel's cache, which could be eating up RAM unnecessarily by c........

Virtualbox is a very powerful tool, but for some use cases it is less than optimal. Say you are in a work, lab or other environment where you are not alone on the physical network and there could be overlap of IPs, but you need all of your VMs to be contactable from your host, VMs need to communicate with each other, and VMs need internet. NAT Network will give you VM to VM communication and internet, however, it is buggy and unstable. It also doesn't allow host to VM co........

Remember that control connections are established on port 1723 and then actual data is transferred over GRE protocol 47. If you have a NAT setup this will work without special forwarding or accepting of GRE packets (normally if you are not blocking outgoing connections and accepting established and related connections). The below two commands will get things going so PPTP and GRE work We first load the ip_nat_pptp module which allows PPTP to work with........

The Best Docker Tutorial for Beginners We quickly explain the basic Docker concepts and show you how to do the most common tasks from starting your first container, to making custom images, a Docker Swarm Cluster Tutorial, docker compose and Docker buildfiles.........

Why choose OpenVPN instead of a firewall appliance? OpenVPN can be a reliable and easy replacement for traditional hardware or just be an additional tool that your company uses so that the firewall can focus on its job rather than acting as a VPNappliance at the same time. When comparing OpenVPN with traditional firewal........

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_........

#if you have nvidia make sure you install the nvidia-cuda-toolkit so hardware acceleration can be used wget http://ffmpeg.org/releases/ffmpeg-3.3.2.tar.bz2 tar -jxvf ffmpeg-3.3.2.tar.bz2 cd ffmpeg-3.3.2/ ./configure --disable-yasm install prefix /usr/local source path ........

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........

I still cannot understand how this would not be enabled by default and I struggled to find the reason why with manually installing samba etc.. wondering why the option for sharing was not in the menu. On Linux Mint "MATE" the package is called "caja-share" and on Cinnamon it is called "nemo-share" so edit the below command as necessary: *Also note that the "samba" package is necessary as it is not inst........

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........

Another new drive bad from the start: Jun 2 15:14:18 one-desktop kernel: [15895.386779] ata2.00: exception Emask 0x50 SAct 0x1 SErr 0x280900 action 0x6 frozen Jun 2 15:14:18 one-desktop kernel: [15895.386782] ata2.00: irq_stat 0x08000000, interface fatal error Jun 2 15:14:18 one-desktop kernel: [15895.386784] ata2: SError: { UnrecovData HostInt 10B8B BadCRC } Jun 2 15:14:18 one-desktop kernel: [15895.386788] ata2.00: cmd 60/0........

This is just trying to read 5GB off the drive with dd and the drive initially tested ok but shortly after I wondered why I was seeing 2MB/s read speeds. Notice the "current_pending_sector", anytime I've seen it at anything above 0 even with no other bad fields/attributes, it means the drive is bad. ata1.00: exception Emask 0x0 SAct 0x3 SErr 0x0 action 0x0 ata1.00: irq_stat 0x40000008 ata1.00: failed command: READ FPDMA QUEUED ata1.00: cmd 60/00:00:........

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.........

Here's a proven example of what a bad hard drive can do, it was technically functioning OKin a RAID array but the system became extremely low and the load become high and IOWAIT was even higher and I always thought it was a bad application. The truth is that this failing 1TBHitachi has slowly gotten worse and caused huge slowdowns, (eg. 100% load on Thunderbird waiting for e-mails to load etc..). After swapping it out, tabs change instantly, emails are not lagged, and........

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........

I like dd, although it only reads it, usually a read test of the entire disk will uncover if your hard drive is bad in some parts. This is a good thing to do at least once a month, a lot of times bizarre program behavior, laginess and crashing/unnmounting problems etc.. are due to a failing disc and SMART won't know it or indicate a problem: We must also remember there's never a guarantee, I've found that ever since we moved to larger and more platters per drive with 1TB drives........

I had a dying drive that smart thought until it totally disappeared was a good drive, and actually all parameters did look fine but this system was causing my system to lockup and other bad behavior: === START OF INFORMATION SECTION === Device Model: WDC WD20EARS-00MVWB0 Serial Number: WD-WMAZ20139 Firmware Version: 50.0AB50 User Capacity: 2,000,398,934,016 bytes Device........

I had one of these shipped and it was not recognized when plugged in, here's what a dead drive looks like (I assume it's teh circuit board which is dead): ata1: link is slow to respond, please be patient (ready=0) ata1: softreset failed (device not ready) ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 300) ata1: link online but device misclassified, retrying ata1: link is slow to respond, please be patient (ready=0) ata1: softreset f........

Let the numbers speak for themselves, from what I read the Load_Cycle_Count which is very high (more than 500,000/half a million times) is the number of head parks. What a stupid"Green" design and design flaw which will probably mean an early life for the drive. This is almost as silly as Seagate's new reputation for BSY/poor quality disks since the 7200.11 series. To make it worse this is also when Western Digital introduced "Advanced Format" o........

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........

This drive is clearly on the way out, the Kernel knows it but I'm surprised that SMART is not concerned. I didn't blame Seagate for their past issues until now. This hard drive has hardly been used and has not even been powered on for a year according to SMART. Home page is http://smartmontools.sourceforge.net/ === START OF INFORMATION SECTION === Model Family: Seagate Barracuda 7200.11 Device........

Seagate Inventory/Firmware Check I heard about this issue a long time ago but never looked into it. I figured I wasn't affected since my 500GB drives were running for so long. I've been using Seagate's since 2002 and to this day all of the drives I have are alive from Seagate. *Update the bad news is that I realize one of my 500GB's is about to die, it's not even a year old, but is also not affected by the recall according to Seagate! Seagate Inventory/Firm........

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........