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.........
Usually if you get the grub boot loader and it doesn't show any boot options, it's because grub was not installed correctly and/or the partition that it is supposed to be on has changed or does not exist. It can also happen if you install Linux to one drive, but the boot loader to another by accident, whether EFI or MBR/Legacy mode.
You can normally fix it by chrooting into your root partition:
#make a direc........
How Do You Apply Changes You've Made?
You can make all kinds of changes to the switch, but remember they are not actually active until you run the "commit" command. This means adding or deleting config options will not have any effect until you run "commit".
Under configure mode:
FATAL: kernel too old
This happens for example if you are in Centos 6 and trying to chroot into a system based on a newer kernel like 4.x+
You'll have to use a newer OS/kernel system to chroot into the environment or a VM running a newer kernel.........
The reason for doing this is that the installer doesn't seem to work properly for LUKS and the server installer doesn't even support LUKS anymore. When you use the GUI install on Desktop for LUKS it won't boot and will just hang after you enter your password. So the only reliable way is to do it ourselves.
1.) Make a default minimal install of Ubuntu
2.) Have a secondary disk on the server or VM.
The cool thing here is that we only need 1 drive to make a RAID 10 or RAID 1 array, we just tell the Linux mdadm utility that the other drive is "missing" and we can then add our original drive to the array after booting into our new RAID array.
Step#1 Install tools we need
yum -y install mdadm rsync
Step #2 Create your partitions on the drive that will be our RAID array
Here I assume it is /dev........
chroot which stands for change root allows you to virtually operate in another operating system even though you haven't booted it. It is commonly used to deploy new distros, applications and to fix a broken Linux/Unix install or prep a new system image without having to physically boot the drive or disk.
So in this example let's say we have a drive that has a Linux OS installed on /dev/sdb1 and we have mounted this partition on /mnt/sdb1
The key point is to edit the &quo........
It was broken because of this package for xorg I installed:
Just remove it even if you have to chroot from a live USB/CD:
sudo apt-get remove xserver-xorg-core-hwe-18.04........
The key thing here is to know the actual partition that is encrypted.
Often in Linux Mint's installer that ends up being partition 5 or /dev/sda5
sudo cryptsetup luksOpen /dev/sda5 anynamehere
You will then be prompted for your irrecoverable passphrase:
Enter passphrase for /dev/sda5:
If all goes well it won't say anything further. If it says ""No key available with this passphr........
In Centos 7 the days of editing the "kernel"line and adding "single"are gone. On top of that sometimes after a new install passwords do not work, maybe you forgot your password or for some other reason you need to break in or fix your system? It could also be because you can't mount your root / or some other /etc/fstab error and many other errors.
1. Edit your grub settings and find the linux16 /vmlinu........
Iam not sure why this is happening neither the hostnode or VM changed. All I did was reboot the hostnode and startup the Centos VM again, also note it happened with the original kernel on the VM and also the latest 6.9 kernel as of this writing as shown below.
Host Node: Centos 6.9
Same result in any kernel above........
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........
1.) Replicate the number of partitions in your new drives.
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).........
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........
Iwas surprised to see that Linux Mint at the latest 17.2 version still has NO mdadm installer option, and worse the installer will not be able to create a proper booting environment even when you do install it.
How to setup mdadm in Linux mint LiveCD
apt-get install mdadm
# partition as you need and then create your mdadm devices
# create your SWAP md0
mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /d........
#count=10000 makes an image of 10000MB make sure your image is at least the same as your existing
dd if=/dev/zero of=yourimage.img bs=1M count=10000
# losetup -fv newimage.raw
# fdisk -cu /dev/loop0
# kpartx -a /dev/loop0
# dd if= of=/dev/mapper/loop0p1
# e2fsck -f /dev/mapper/loop0p1
# resize2fs /dev/mapper/loop0p1
# a lot of guides tell you to edit /etc/fst........
mount -o bind /proc /sda2/proc
mount -o bind /dev/ /sda2/dev
mount -o bind /sys /sda2/sys
mint / # mount -o bind /proc /sda2/proc
mint / # mount -o bind /dev/ /sda2/dev
mint / # mount -o bind /sys /sda2/sys
mint / # chroot /sda2
mint / # cd ~
mint ~ # ls
mint ~ # cd /
mint / # ls
bin Desktop dev-temp home&nb........
This booting error is because the Xen PV guest image uses the Xen kernel, this is not compatible with anything but a host running a Xen kernel.
I did a kpartx -av virtual.img and then it created some partitions that showed up in fdisk.
I mounted it and did a chroot into it and removed the xen kernel and installed a normal kernel but Xen still shows the same kernel in Grub (only the Xen one).
This is strange but it seems like this Xen PV guest has some sort of hidden or........
Moving to RAID was a pain.
What you have to do is the following from an existing install:
Create your mdadm RAID 1 array on your spare hard drive.
Start it with the missing disk.
rsync the entire contents of your current / to the md partition.
Here's a good way of doing it:
rsync -Pha --exclude=/proc/* --exclude=/sys/* --exclude=/mnt/* /. /mnt/md2........
From a LiveCD or if you're doing something like converting your non-RAID install to mdadm here's how you would chroot properly (you have to mount your proc, sys and dev on the running system/LiveCD to your chroot environment if you want things to work right, especially if you need to run update-initramfs due to a driver change etc..)
*replace "path" with your mount/chroot path
mount -o bind /proc /mnt/path/proc
mount -o bind /dev/ mnt/pa........
This was done on Centos butI think it's easier on Debian machines, the paths that it is set to use are tailored towards Debian, so there is some fiddling that needs to be done on Centos.
This is for chrooting ssh, but jailkit has other uses than just SSH jails but I won't cover them in this writeup.
1. Install jailkit
yum install jailkit
2. Setup Jail Home
chown root:root /home/ja........
I wasted a lot of time wondering why I could never find those packages.
Check the /etc/yum.conf file and at the bottom look for the "exclude=" line.
Below is what I found in mine
exclude=apache* httpd* mod_* mysql* MySQL* da_* *ftp* exim* sendmail* php* bind-chroot*
Just remove those entries or uncomment that line and you'll get access to the missing applications.........
I installed 5.5 with a 300GB RAID 1 partition (boot is also on this partition). It booted up fine the first few times until after I used a Live CD and accessed the array, and it became named /dev/md127 for some reason.
Now whenI boot into CentOS I get a kernel panic and different errors, once I got "invalid superblock", even though the array is fine (it didn't happen again, probably because I was sure to dismount and stop the mdadm array properly).
It's not just as simple as running the chroot command, you need to ensure the /proc and /dev entries are passed through and populated to the chroot environment.
Step 1 - Mount Your Off-lineOS
mount /dev/sda1 /mnt
Step 2 - Mount Proc
mount -t proc none /mnt/proc
Step 3 - Mount Dev
Most guides will tell you to use this: mount -o bind /dev /mnt//dev but that doesn't work for some reason in many cases:
I decided on using yum to help me decide even though I normaly use proftpd I decided to see what else I could find.
yum search ftp
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* rpmforge: ftp-stud.fht-esslingen.de
* base: mirrors.netdna.com
* updates: updates.interworx.info
* addons: yum.singlehop.com
* extras: mirrors.netdna.com