RAID Volume not accessible in Linux

Typically your RAID volumes will show up as /dev/mdXXX

If it is not, it could be because the device mapper module is not loaded.  Load it by running the following command.

modprobe dm-mod

As a side note you can list the block devices using

dmraid -b

https://bbs.archlinux.org/viewtopic.php?id=42321

If your still having trouble you can try installing mdadm and dmraid

apt-get install -y dmraid mdadm

 

Delete SNMPv3 User on Linux

Don’t know if this is the recommended way to delete a user, but it seems to work.

sudo service snmpd stop

Open up the snmpd.conf file in /var/lib and find the line with the SNMP user and delete the line

sudo vi /var/lib/snmp/snmpd.conf

The above file may be in the following location on RPM based systems.

sudo vi /var/lib/net-snmp/snmpd.conf

Save, exit, and start snmpd

sudo service snmpd start

These steps work for Ubuntu, but should work for any Debain based distro as well as CentOS, Fedora, RedHat etc.

Install dig on Ubuntu, Debian or Kali Linux

install dig
Help options for dig


Dig is a DNS lookup utility.  It is included in most Linux distributions by default, but if it isn’t you can easily install dig with the following command.

The dig utility is apart of the dnsutils package

sudo apt-get install dnsutils -y

After it is installed, we can verify that it is working with

dig -v

For more information on how to use dig, refer to the following link.

https://www.howtogeek.com/663056/how-to-use-the-dig-command-on-linux/

The following is copied and pasted from the dig man page.

NAME
       dig - DNS lookup utility

SYNOPSIS
       dig [@server] [-b address] [-c class] [-f filename] [-k filename] [-m] [-p port#] [-q name]
           [-t type] [-v] [-x addr] [-y [hmac:]name:key] [[-4] | [-6]] [name] [type] [class]
           [queryopt...]

       dig [-h]

       dig [global-queryopt...] [query...]

DESCRIPTION
       dig is a flexible tool for interrogating DNS name servers. It performs DNS lookups and
       displays the answers that are returned from the name server(s) that were queried. Most DNS
       administrators use dig to troubleshoot DNS problems because of its flexibility, ease of use
       and clarity of output. Other lookup tools tend to have less functionality than dig.

       Although dig is normally used with command-line arguments, it also has a batch mode of
       operation for reading lookup requests from a file. A brief summary of its command-line
       arguments and options is printed when the -h option is given. Unlike earlier versions, the
       BIND 9 implementation of dig allows multiple lookups to be issued from the command line.

       Unless it is told to query a specific name server, dig will try each of the servers listed
       in /etc/resolv.conf. If no usable server addresses are found, dig will send the query to the
       local host.

       When no command line arguments or options are given, dig will perform an NS query for "."
       (the root).

       It is possible to set per-user defaults for dig via ${HOME}/.digrc. This file is read and
       any options in it are applied before the command line arguments. The -r option disables this
       feature, for scripts that need predictable behaviour.

       The IN and CH class names overlap with the IN and CH top level domain names. Either use the
       -t and -c options to specify the type and class, use the -q the specify the domain name, or
       use "IN." and "CH." when looking up these top level domains.

SIMPLE USAGE
       A typical invocation of dig looks like:

            dig @server name type

       where:

       server
           is the name or IP address of the name server to query. This can be an IPv4 address in
           dotted-decimal notation or an IPv6 address in colon-delimited notation. When the
           supplied server argument is a hostname, dig resolves that name before querying that name
           server.

           If no server argument is provided, dig consults /etc/resolv.conf; if an address is found
           there, it queries the name server at that address. If either of the -4 or -6 options are
           in use, then only addresses for the corresponding transport will be tried. If no usable
           addresses are found, dig will send the query to the local host. The reply from the name
           server that responds is displayed.

       name
           is the name of the resource record that is to be looked up.

       type
           indicates what type of query is required — ANY, A, MX, SIG, etc.  type can be any valid
           query type. If no type argument is supplied, dig will perform a lookup for an A record.


					

Allow KDE Connect through firewall

Firewalld

sudo firewall-cmd --zone=public --permanent --add-port=1714-1764/tcp
sudo firewall-cmd --zone=public --permanent --add-port=1714-1764/udp
sudo systemctl restart firewalld.service

UFW firewall

sudo ufw allow 1714:1764/udp
sudo ufw allow 1714:1764/tcp
sudo ufw reload

More information https://community.kde.org/KDEConnect

Recovering LibreNMS from crashed XenServer VM

Had a LibreNMS instance crash, or the VM crashed, not bootable anymore.  Was able to boot it up on a CentOS iso with rescue mode, which gave me access to the files.  So the idea is to manually copy off the LibreNMS files and LibreNMS database and import them to a new LibreNMS instance

Issues

  • Need to access the the system files
  • MySQL doesn’t start in a chroot environment, so no way to do a mysqldump —  (Has to do with systemv or something)

Steps

  1. Create new LibreNMS VM with a new instance of LibreNMS installed
  2. Gain access to the crashed system
  3. Copy over LibreNMS MySQL databases to new LibreNMS instance
  4. Copy over LibreNMS files “/opt/librenms” to new LibreNMS instance
  5. Clean up.  Set users on directories, check SELinux etc.

1. Installing New LibreNMS VM

  • Guide for Ubuntu/Debian distro’s here
  • Guide for for Fedora/CentOS/RedHat here

2. Gaining access to crashed VM

There can be a couple of ways to gain access to a crashed XenServer VM.  One of the easiest ways is to boot up in recovery mode and go through the installers rescue mode.  Guide to boot up XenServer VM in recovery mode here.

The installer rescue mode should detect the OS and mount everything.  If not you should be able to mount the root partition manually.

Once booted up, you’ll need to enable network access if your going to use sftp or scp to copy files.  There are a few different ways to do this

  • Run “dhclient” to pull an address via DHCP
  • Set a static IP address
    • Guide for Ubuntu/Debian distro’s here
    • Guide for fedora/CentOS/RedHat here

3.Copy LibreNMS Mysql Database

Backup the LibreNMS MySQL database directory

tar czvf librenms_mysql.tgz /var/lib/mysql

Use scp or sftp to copy it to the new LibreNMS instance

scp librenms_mysql.tgz user@new_LibreNMS_ip

Now on the new LibreNMS instance we need to run the following few commands

systemctl stop mariadb
rm -rf /var/lib/mysql/*
tar xzvf librenms_mysql.tgz -C /
chown -R mysql:mysql /var/lib/mysql

4. Copy LibreNMS directory

Backup the LibreNMS directory

tar czvf librenms.tgz /opt/librenms

Use scp or sftp to copy it to the new LibreNMS instance

scp librenms.tgz user@new_LibreNMS_ip

Now on the new LibreNMS instance we need to run the following few commands

rm -rf /opt/librenms/*
tar xzvf librenms.tgz -C /
chown -R librenms:librenms /opt/librenms

5. Clean up

Disable SELinux if you have not already.  Guide here

Restart apache, and start mysql.  If your on Ubuntu, the services are named apache2 and mysql

systemctl restart httpd
systemctl restart mariadb

That should get it working, if not try a reboot.

Special notes

The whole MySQL directory needs to be copied, there are innodb files that will keep MySQL from starting if they are not copied.

There is some good info here
https://stackoverflow.com/questions/1795176/how-to-change-mysql-data-directory

Auto mount CIFS mount point on system startup on Ubuntu

Install CIFS utils

sudo apt-get install -y cifs-utils

You can manually test it with the following command.  Change the ip address, mount points, username, and password.

mount.cifs /192.168.1.102/mount/point /mnt -o user=john,pass=password3,uid=john

Note that specifying the uid in the options, allows the user to add, delete, and modify the files and folders of that specific mount point.

To auto mount on system startup, add the following line to /etc/fstab.  Change the appropriate lines.

//192.168.1.102/mount/point   /mnt  auto   user=john,pass=password3,uid=john   0   0

You can test it by mounting everything in fstab

sudo mount -a