• ssh how to verify your host key / avoid MIM attacks


    SSH helps keep us secure in many ways, one of those is the host-key fingerprint which is unique. If you have been connecting to an SSH server that you've made no changes to and suddenly ssh warns that the key doesn't match then you have a problem. But how about connecting to an existing server for the first time on a new machine or client? A lot of new clients calculate it using an SHA256 hash but it is not as easy on your host machine to produce the sam........
  • Linux What is umask (user mask) for file and directory creation permissions and how to calculate umask and change the defaults


    umask are the default permissions that are applied when a file or directory are created. To see this in action simply just "touch filename" or "mkdir somedir" and you'll see what default permissions are applied. The first thing Ialways tell people you should know is to NEVER change the defaults unless you are making them more restrictive. But they work well and if you change the defaults you could end up creating a file without permission to read........
  • VMWare ESXi 6.7 SSH/PowerShell CLI Commands


    [root@localhost:~] BootModuleConfig.sh echo host-ind nfcd........
  • Debian Mint Ubuntu compiling xmr-stak


    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........
  • wodim / cdrecord error cannot burn DVD or BDR .iso Errno: 5 (Input/output error), write_g1 scsi sendcmd: no error


    dvd+rw-mediainfo /dev/sr0 INQUIRY: [ASUS ][BW-16D1HT ][3.00] GET [CURRENT] CONFIGURATION: Mounted Media: 11h, DVD-R Sequential Media ID: RITEKF1&n........
  • linux mint image convert menu option missing solution


    Ialready have the caja-image-converter option installed but it shows nothing. Weirdly enough if you install nemo and nautilus converter it does show and work inside caja: The solution is to install *-image-converter sudo apt-get install *-image-converter Reading package lists... Done Building dependency tree Reading state information... Done Note, selecting 'n........
  • VMWare 6.7 VCSA VSphere ESXi Management SSO Install Guide on Linux using the CLI


    #mount the VCSA DVD mount /dev/sr0 /mnt/cd #alternatively you could mount the iso directly mount -o loop vcsa.iso /your/mount/path #for this purpose we are using the CLI installer on Linux cd /mnt/cd/vcsa-cli-installer/lin64 #no it's not going to be that easy you can't just run vcsa-deploy like that you need to use a template or configured .json file ./vcsa-deploy Usage: vcsa-deploy [-h] [--version] [--supported-deploymen........
  • Linux Mint Black Screen after boot no graphics solution


    This is not the normal "black screen"issue and I was shocked to eventually find out why. The normal advice of reconfiguring Xorg didn't work. Even booting into "Recovery Mode" did not help. Here is the short end of the stick that fixed it: sudo apt-get install mdm mate-desktop-environment Yes you got it right, mdm and the mate-desktop-environment / gnome were somehow uninstalled. This must be whe........
  • bash Linux how to get first or last letters of a word


    To get the first X letters of a word: It's very simple you can just pipe it to head with -c 1 (gives the first letter and so on) -c2 (2 gives the first 2 letters). echo "dsjfsdlksjdklf;jlsd;kflasdj;kl"|head -c 2 Returns ds To get the last X letters of a word: Now we use tail with -c but it works differently. ........
  • ffmpeg Unable to Use Hardware Encoding with Nvidia 3.40 Driver and GT210 card


    I believe from what I've read that this card's driver doesn't support the features after trying all known troubleshooting methods. ffmpeg -i uservideoRendered.mp4 -filter:v hwupload_cuda,scale_npp=w=1920:h=1080:format=nv12:interp_algo=lanczos,hwdownload -c:v hevc_nvenc -profile main -preset slow -rc vbr_hq -c:a copy uservideoRendered.mp4-test ffmpeg -i uservideoRendered.mp4 -filter:v hwupload_cuda,scale_npp=w=1920:h=1080:format=nv12:interp_algo=lanczos,hwdownload........
  • Migrate Centos 7 from Single HDD to mdadm RAID 10 array:


    Done on Centos 7.3 very important as clearly based on older guides it was a lot easier and more simpler! Hint do not use grub2-install! One huge caveat if you are an oldschool user or sysadmin who has avoided UEFIbooting The normal way will not work here if your Centos was using UEFI. Newer systems use it by default. The easiest way to check is to do an fdisk -l if your sy........
  • USB 3.0 External HDD Enclosure Seagate UAS problems - [sdd] tag#1 CDB: Write(16) 8a 00 00 00 00 01 70 04 08 68 00 00 00 08 00 00


    This is a 8TB Seagate external USB 3.0 device apparently newer kernels use a module called "UAS" instead of "USB Storage" which causes issues as a lot of devices are not properly supported in UAS mode by the kernel driver. The solution some say is to disable UAS specifically for your USB device but I'd rather just disable UAS altogether. Solution blacklist UAS: *do not do this it does not work and just causes your USB 3.0........
  • mencoder bmovl error vf_bmovl: Unknown command: ''. Ignoring.


    Based on this tutorial: http://www.linuxjournal.com/content/overlay-images-video-using-mplayer-and-mencoder mencoder -oac pcm -ovc raw -vf bmovl=0:0:tfifo -o $output $file vf_bmovl: Unknown command: ''. Ignoring. ........
  • Migrating from Linux Mint 17.2 mdadm RAID array to a new one (because I upgraded to larger drives).


    1.) Replicate the number of partitions in your new drives. gdisk /dev/sda gdisk /dev/sdb I created 3 partitions of the same same size. partition #1: +1G (/boot) partition #2: +60G (swap) partition #3: rest of it (/) #note if you are using GPT/gdisk you need to create separate a partition at least 1MB in size (in my case I would a 4th partition and mark it type ef02).........
  • DRBD Split-brain solution


    Uh oh [17925926.174277] block drbd0: Handshake successful: Agreed network protocol version 96 [17925926.174325] block drbd0: conn( WFConnection -> WFReportParams ) [17925926.174342] block drbd0: Starting asender thread (from drbd0_receiver [1682]) [17925926.174432] block drbd0: data-integrity-alg: [17925926.174581] block drbd0: drbd_sync_handshake: [17925926.174586] block drbd0: self 2AAE66AF9252D6DB:2815BF........
  • Centos 6 how to guide convert LVM non-RAID into mdadm 1/10 RAID array live without reinstalling


    Here is the scenario you or a client have a remote machine that was installed as a standard/default minimal Centos 6.x machine on a single disk with LVM for whatever reason. Often many people do not know how to install it to a RAID array so it is common to have this problem and why reinstall if you don't need to? In some cases on a remote system you can't easily reinstall without physical or KVM access. So in this case you add a second physical or disk or already ha........
  • LVM Tutorial how to create a Physical Volume (PV), Volume Group (vg), and a Logical Volume (LV) within it


    # first we need a physical volume which we use the pvcreate tool to create # I create mine on /dev/sdb3 pvcreate /dev/sdb3 dev_is_mpath: failed to get device for 8:19 Physical volume "/dev/sdb3" successfully created # pvdisplay shows the newly created volume pvdisplay "/dev/sdb3" is a new physical volume of "1.35 TiB" --- NEW Physical volume --- PV N........
  • LSI MegaRAID Adventures, Guide and HowTo


    LSi Megaraid At first it was configured as a RAID 0, then I deleted the Virtual Disk Group. I thought both drives would be shown and detected in Linux as sda and sdb but it actually shows nothing. To make them work you have to hit Ctrl+R before the system boots (when prompted) and create a Virtual Disk Group. In my case I created each one as RAID 0 (with a single drive only) as I just wanted JBOD but there is no such option or default in these Dell Pe........
  • yum update error


    yum update error Traceback (most recent call last): File "/usr/bin/yum", line 29, in ? yummain.user_main(sys.argv[1:], exit_code=True) File "/usr/share/yum-cli/yummain.py", line 229, in user_main errcode = main(args) File "/usr/share/yum-cli/yummain.py", line 145, in main (result, resultmsgs) = base.buildTransaction() &nbs........
  • Linux High IOWAIT updatedb can't be killed and crash with mdadm


    high IO wait 424 root 39 19 1900 848 552 D 0.0 0.0 0:00.91 updatedb root 424 0.0 0.0 1900 848 ? DN Mar11 0:00 /usr/bin/updatedb -f sysfs?rootfs?bdev?proc?cpuset?binfmt_misc?debugfs?sockfs?usbfs?pipefs?anon_inodefs?futexfs?tmpfs?inotifyfs?eventp........
  • Apache MPM worker vs prefork


    find what MPM Apache is using, it will either be using "worker" or "prefork" apachectl -l Compiled in modules: core.c prefork.c http_core.c mod_so.c In my case it is "prefork" vi /etc/httpd/conf/httpd.conf Find the section that looks like this (by default one will normally exist for prefork and for worker, but in my case I only care a........
  • SolusVM/Xen Central Backup Warning - Takes System Off-line!


    This really gives me a bad impression of SolusVM. I tried the "Central Backup" option and it does not warn that your server gets shutdown instantly in order to do the backup! Further, there is no way to pause or cancel the backup. Thankfully this is a test/small disk usage VPS but what if someone was running something production with a large filesize? Ihaven't used QuickBackup but hope that isn't the same thing. Everyone should be vary car........
  • LUKS/cryptsetup Tutorial for Linux Hard Drive Partition Encryption


    This is based on Debian Linux but should apply equally to any *nix distro. Install LUKS/crypt-setup apt-get install cryptsetup Setup your LUKS Partition Of course change /dev/md2 with whatever partition you intend to use LUKS on. cryptsetup --verbose --verify-passphrase luksFormat /dev/md2 You'll be asked to verify your decryption password twice *DO NOT FORGET THIS PASSWORD AS IT IS NOT RECOVERABLE!........
  • Use rcconf to edit startup/init.d/init scripts on Debian/Ubuntu based distributions


    I've never understood how to enable and disable services for different run levels in Debian based distros, it's just weird, annoying and doesn't make sense. I much prefer chkconfig from RHEL. Just install the package called 'rcconf' and be done with it. rcconf makes things easy for you. apt-get install rcconf Reading package lists... Done Building dependency tree Reading state information... Done........
  • Convert HDD/Hard Drive Partition(s) into non-RAID into RAID 1 using existing data without data loss and without reformatting.


    Before we start I take no responsibility for this, you should have a backup and if you make a mistake during this process you could wipe out all of your data. So backup somewhere else before starting this as a precaution, or make sure it's data you could afford to lose. The RAID 1 Setup (Hardware Wise) I've already setup my 2 x 1TB (Seagate) drives with identical partitions, make sure your new hard drive (the empty one) is setup like your curr........
  • Linux EXT3 16GB-17GB maximum filesize issue solved/how to fix


    I have no idea why but mkfs.ext3 defaults to a patheticlly small blocksize of 1024 bytes/1KB (kilobyte). That means the maximum filesize is ONLY 16GB! With 2KB/2048 bytes you get a 256 GB maximum filesize, and with 4KB/4096 bytes you get 2TB! I finally noticed/paid attention to this after realizing that with rsync and scp that no file larger than 17GB could be transferred. I then realized it must be a file size limit on the partition. Here is what tune2fs tol........
  • PHP cannot access /usr/bin/openssl


    PHP cannot access /usr/bin/opensslI have verified the username that runs the process is able to access /usr/bin/openssl and it does exist but the PHP script is saying it doesn't exist: [code:1:1fd0f3abbe] if (!file_exists($OPENSSL)) { //echo "ERROR: OPENSSL $OPENSSL not foundn"; }[/code:1:1fd0f3abbe] I don't get itI can clearly see the contents of /usr/bin by using the PHP system fu........
  • Configuring OCFS2 Clustered File System on Debian Based Linux including Ubuntu and Kubuntu


    There's a lot of information and guides on OCFS2 for RHELand Centos Linux but the package setup and configuration is slightly different and this has thrown some people off. Installing OC2FS You should install the following packages to get started: apt-get install ocfs2-tools ocfs2console Configure OC2FS In RHEL/Centos the main configuration file is located in /etc/sysconfig/o2cb However in Debian based Linux it is located........
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