Blog, Linux
Reduce the size of a partition containing an volume
mdadm --grow /dev/md0 --size=122G
Check the filesystem on mdadm raid volume
e2fsck -f /dev/md0
Stop the raid device
mdadm /dev/md0 --stop
Resize the physical partition (use GParted to do that)
You may need to boot from a Live CD to do this – to use parted, you may not have to reboot to a live image
You can also use the parted command line tool as follows:
# apt install parted
parted /dev/sda
(parted) print
# IMPORTANT: The END is NOT the new size - you have to add sizes of partitions before it
(parted) resizepart
Partition number? # Select partition number to resize
End [10G]? # Enter the new end of partition in bytes (remember to add sizes of partitions before it)
# Also, double check in GParted to make sure the size is what you expect it to be, since
# the parted size does not correspond to GParted size
# The short sintax is (assuming partition number is 2 and you need it to resize to 125G):
(parted) resizepart 2 125G
# To continue to the next drive, use select
(parted) select /dev/sdb
https://www.tecmint.com/parted-command-to-create-resize-rescue-linux-disk-partitions/
Start the raid device
mdadm --examine --scan
mdadm --assemble --scan
#mdadm --assemble /dev/md0 /dev/sda1 /dev/sdb1
In case of a raid 1 device not starting up, you might mount one of the raid partitions as a standard partition, then
create a new raid one drive using the second partition. If that works, you can sync from the standard device to the
new raid device and afterwords add the second partition to the raid, which will cause the raid to recover.
# Assume /dev/sda3 and /dev/sdb3 was devices of the raid 1 array that is now broken
mkdir /mnt/sdb3
mount /dev/sdb3 /mnt/sdb3 # Assuming sdb3 was a raid 1 device and filesystem is still in tact.
mdadm --create --verbose --force /dev/md1 --level=mirror --raid-devices=1 /dev/sda3
rsync -avz /mnt/sdb3/* /mnt/md0/
mdadm --manage /dev/md0 --add /dev/sda3
cat /proc/mdstat
References
Blog, Linux
To list installed server libraries, execute the following SQL: show shared_preload_libraries. To configure
libraries to be preloaded, edit postgres.conf. On an Ubuntu apt installation, it would typically be found in
/etc/postgresql/9.0/main.
To see the default dynamic library search path, execute the following SQL: show dynamic_library_path
$libdir is configured during compile time. On an Ubuntu installation which is done using an Ubuntu package,
$libdir will typically point to /usr/lib/postgresql/9.0/lib. Plug-in library files should typically
be put in /usr/lib/postgresql/9.0/lib/plugins on an Ubuntu system.
To automatically create objects when a new database is created, create the objects in template1. (template0 is
barebone template from which template1 is created)
To install the PL/PGSQL debugger in an Ubuntu postgres server which has been installed using apt, you might want to do
a one-click install from Enterprise DB on a Linux VM
(see Enterprise DB downloads) and do the following:
Copy /opt/PostgreSQL/9.0/lib/postgresql/plugins/plugin_debugger.so to $libdir/plugins on the Ubuntu installation.
Copy /opt/PostgreSQL/9.0/lib/postgresql/pldbgapi.so to $libdir on the Ubuntu installation.
Copy /opt/PostgreSQL/9.0/lib/postgresql/targetinfo.so to $libdir on the Ubuntu installation.
Copy /opt/PostgreSQL/9.0/share/postgresql/contrib/pldbgapi.sql to /usr/share/postgresql/9.0/contrib. on the Ubuntu installation.
Now edit postgres.conf and change the following setting:
shared_preload_libraries = ‘$libdir/plugins/plugin_debugger.so’
Now restart the postgres server and apply
You can also download the latest version of edb-debugger from
PgFoundry and compile it to get plugin_debugger.so and pldbgapi.sql.
Blog, Linux
MikroTik WiFi CAP Configuration
- Terminology
- CAP device is the abbreviation for Controlled Access Point
- CAPsMAN is the CAP manager and has an enabled CAPsMAN service
- WinBox is a desktop application for managing Mikrotik devices
WinBox can be installed on Linux as a snap package and is probably
the easiest way to connect to a Mikrotik device, since it uses Layer 2 network
communication and therefore does not require an IP address in the LAN subnet.
- MikroTik device
When MikroTik device is first powered up, the default IP address is
192.168.88.1, admin password is empty and the SSID
is Mikrotik. If LAN subnet is different, the easiest way
to change configuration is to connect via WiFi to open the web
configuration at 192.168.88.1.
- Select Quick Set (top right) and select CAP in combobox just below
- Configure network address
- Choose MikroTikCAPsMAN as router identity
- Select Bridge All LAN Ports as router identity
Use UP arrow to revert back to default in options to follow when setting up a configuration
or device settings which refers to some other configuration.
- CAPsMAN manager device
- CAP device (controlled by CAPsMAN)
The easiest way to configure a CAP device is by connecting via WinBox and
linking the device to a CAPsMAN manager.
- Connect to the device using WinBox
- Navigate to Quick Set using the menu on the left
- Set mode (combo box at top) to CAP
- Set Address Acquisition to Automatic
- Set Address Source to Ethernet
- Select Bridge All LAN Ports
- Set Router Identity to a unique name on the LAN
- Change password
- Press OK
- Navigate to Wireless using the menu on the left
- Select the WiFi Interfaces tab
- Press CAP button
- Select Enabled
- Set Interface to wlan1
- Set Certificate to none
- Set Discovery Interface to ether1 (if devices are linked via ethernet)
- Set Bridge to bridgeLocal
- Press OK
- References:
Blog, Linux
Recover a Linux installation after loosing the administrator user password
- Download a Linux live CD
It can be any linux distro as long as your architecture is the same as the installation.
Lets go with Ubuntu desktop, because instructions may be slightly different for different
distros.
https://ubuntu.com/download/desktop/thank-you?version=20.04.2.0&architecture=amd64
- Burn the ISO to a CD
- Boot the machine with lost password from the CD
In the case of Ubuntu, you will have the option to “Install Ubuntu” or “Try Ubuntu”.
Select “Try Ubuntu”, otherwise you risk formatting your disk(s).
(You might have to select a language somewhere in the process)
- Start terminal
When Ubuntu desktop is ready, click on “Activities” or press the Windows button. When
activity search appears, type “term” – the “Terminal” app should appear – open it.
- From the terminal, execute the following:
sudo bash
# You should now be "root" user
Find disks and partitions
Use any combination of the following commands to get information about partitions:
fdisk -l
lsblk
Valid entries should look like this:
/dev/sd*
/dev/nvme*
Create a mount point to work with
mkdir -p /mnt/linux
Figure out on which drive Linux is installed
The partion where Linux is installed, should typically have an “ext4”
filesystem if it is a recent version of Ubuntu, but it may be different if
other options or distros were installed. Here is an example of how you would
check if a partition (e.g. /dev/sda1) contains linux:
mount /dev/sda1 /mnt/linux
ls /mnt/linux/boot
If anyone of these fails, Linux is not on it. You can umount the partition with the following command
if this is the wrong partition before moving on to check another partition:
umount /mnt/linux
Having found a Linux partion, do the following:
chroot /mnt/linux
If this fails, this is not the partition you are looking for. However, if the installation is a x86 installation
it will not work if you booted an amd64 cd. The error message should be very clear and you should
then download an older version of Ubuntu or Lubuntu that is x86 – you can use this link:
https://cdimage.ubuntu.com/lubuntu/releases/18.04.5/release/lubuntu-18.04.5-desktop-i386.iso
Add user or change password
If the chroot command succeeded, you should now be root user in the installed linux and you
can manipulate the users and configuration. To create a temp user with admin rights, do the following:
useradd -d /home/tempadmin -m -s /bin/bash -g users -G sudo tempadmin
passwd tempadmin
(You can also change existing user passwords using passwd command)
Now edit ssh configuration to make sure you can log in via ssh: (this tutorial
assumes openssh-server was installed on the machine.
nano /etc/ssh/sshd_config
You need to comment out “AllowUsers” or “AllowGroups” lines, since they might block your new user.
You also need to enable “PasswordAuthentication yes”
On the server in question, the rest of the settings should be ok. Save the and close the file (Ctrl+X)
Unmount the partition
unmount /mnt/linux
You can now and reboot normally
Once machine is booted completely, follow these steps:
- First log in with your newly created username
- Open a terminal and get the address with one of the following commands:
ip a
ifconfig
Check whether routing and DNS is configured correctly:
ping 8.8.8.8
ping www.google.com
Test ssh access
Now you can test ssh access using the address you got earlier trying to ssh to the machine from a different workstation.
ssh tempadmin@
If the only other machine you have is a Windows without Linux For Windows installed, you can download Putty from
https://www.ssh.com/ssh/putty/download
Check if the user has administrator access
The last thing you need to check is if the user is an administrator:
sudo bash
whoami
You would need to enter your password, but then whoami should report
that you are root.
Disclamer: Anyone using any of these instructions do so at their own risk. Neither the author or anyone or any company related to this site takes any responsibility for effects performing any of the tasks on any device.
Blog, Linux
Get information of underlying hypervisor from Linux VM
Execute the following command in the VM
sudo dmidecode | grep -i -e manufacturer -e product -e vendor
