Rotate Raspberry Pi 3 output display to potrait

How to rotate Raspberry Pi 3 output display to Potrait.

1. Edit /boot/config.txt
    # nano /boot/config.txt
  
    Add the following line to the bottom of the line
    display_rotate_1         <= this is to rotate the display output to 90 degrees

    Ctrl + X and type Y    <= to save the updated file

2. Allocate more memory to the GPU from 64M to 128M
    # sudo raspi-config

    In Raspberry Pi Software Configuration Tool, select Advanced Options.
    Select "A3 Memory Split" change it from 64 to 128.
    Press Tab and select <Ok>

bzip2: Cannot exec: No such file or directory

Error when trying to create tar.bz2 Archive File in CentOS 7

The following is the error output when trying to create tar.bz2 file in CentOS7:

$ tar cvfj testfile.tar.bz2 ./testfile*
tar (child): bzip2: Cannot exec: No such file or directory
tar (child): Error is not recoverable: exiting now
tar: Child returned status 2
tar: Error is not recoverable: exiting now
$

First step is to check if the package is installed or not.
$ sudo yum list installed | grep bzip2

If package is not installed, please run the following:
# yum install bzip2
# exit

Then create tar.bz2 file.
$ tar cvfj testfile.tar.bz2 ./testfile*

Issue: CentOS 7 network not in VirtualBox

Issue: Fresh installed CentOS 7 network interface not working.

[root@localhost slean]# ip addr
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
   link/ether 08:00:27:c8:da:c2 brd ff:ff:ff:ff:ff:ff
[root@localhost slean]#

As you can see the interface doesn't have IP address.

To fix this issue, first edit the network interface.  nmtui is a network manager tool user interface.
[root@localhost slean]# nmtui

Select the interface and click "Edit".

Enable the DHCP by setting the Automatically connect and make sure the IPv4 CONFIGURATION to <Automatic>.

Click <OK> and <Quit>.

[root@localhost slean]# system restart network

[root@localhost slean]# ip addr

Source: krizna.com

Commands to check CentOS version

These are the commands on CentOS to check version:

# hostnamectl
# rpm --query centos-release
# cat /etc/centos-release
# cat /etc/os-release
# cat /etc/redhat-release
# cat /etc/system-release

Note:
# uname -a
and
# uname -r
will not give the OS version in detail.

[root@localhost slean]# hostnamectl
      Static hostname: localhost.localdomain
              Icon name: computer
                   Chassis: n/a
            Machine ID: e6450196561343d9976ba0d9c29c54c0
                  Boot ID: 0ddca677a08a44019c0f9b71fec2882a
         Virtualization: vmware
  Operating System: CentOS Linux 7 (Core)
       CPE OS Name: cpe:/o:centos:centos:7
                    Kernel: Linux 3.10.0-229.11.1.el7.x86_64
           Architecture: x86_64
[root@localhost slean]#

Similar result from running # hostnamectl on Oracle VirtualBox

[root@localhost ~]# hostnamectl

   Static hostname: localhost.localdomain

         Icon name: computer-vm

           Chassis: vm

        Machine ID: ec0ea531f8894f84b9d5266ee38dfd8a

           Boot ID: d1fa0335dab445fca139710b318734a8

    Virtualization: oracle

  Operating System: CentOS Linux 8 (Core)

       CPE OS Name: cpe:/o:centos:centos:8

            Kernel: Linux 4.18.0-193.14.2.el8_2.x86_64

      Architecture: x86-64

[root@localhost ~]#

Another way to get the CentOS version is by 

[slean@localhost ~]$ cat /etc/os-release

NAME="CentOS Linux"

VERSION="7 (Core)"

ID="centos"

ID_LIKE="rhel fedora"

VERSION_ID="7"

PRETTY_NAME="CentOS Linux 7 (Core)"

ANSI_COLOR="0;31"

CPE_NAME="cpe:/o:centos:centos:7"

HOME_URL="https://www.centos.org/"

BUG_REPORT_URL="https://bugs.centos.org/"

CENTOS_MANTISBT_PROJECT="CentOS-7"

CENTOS_MANTISBT_PROJECT_VERSION="7"

REDHAT_SUPPORT_PRODUCT="centos"

REDHAT_SUPPORT_PRODUCT_VERSION="7"

[slean@localhost ~]$ 

The next 3 commands give the same output result

[slean@localhost ~]$ cat /etc/centos-release

CentOS Linux release 7.1.1503 (Core) 

[slean@localhost ~]$ 

[slean@localhost ~]$ cat /etc/redhat-release

CentOS Linux release 7.1.1503 (Core) 

[slean@localhost ~]$ 

[slean@localhost ~]$ cat /etc/system-release

CentOS Linux release 7.1.1503 (Core) 

[slean@localhost ~]$ 

Source: https://linuxconfig.org/how-to-check-centos-version

Python Notes

To find out where Python is installed in your Linux machine run the following commands:

~$ which python
/usr/bin/python

~$ which python3
/usr/bin/python3

To find out what Python version is running in your Linux box, run the following commands:

~$ python -V
Python 2.7.6

~$ python3 -V
Python 3.4.3

To start programing Python, run the following command:

~$ python
Python 2.7.6 (default, Jun 22 2015, 17:58:13)
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.

>>>

Use exit() or Ctrl-D (i.e. EOF) to exit

>>>

To exit type the following

>>> exit()

~$

~$ python3

Python 3.4.3 (default, Oct 14 2015, 20:28:29)

[GCC 4.8.4] on linux

Type "help", "copyright", "credits" or "license" for more information.

>>> exit()

~$ 

Configure a Cisco Router to act like a Frame Relay Switch

First of all, information on this page is copied over from Tekcert website.  Another good link regarding configuring Cisco Router as a Frame Relay switch can be view from this link.
This page will show how to configure a regular Cisco Router to work like a Frame Relay switch.  This router will provide Frame Relay switching to 4 other remote routers.

The following is the diagram of the frame relay topology:

In the following section, I will only include the running config that make the router a frame relay switch:
   !
   interface Serial0/0
    description Link to R1
    no ip address
   encapsulation frame-relay
   serial restart-delay 0
   clock rate 64000
   no frame-relay inverse-arp
   frame-relay lmi-type ansi
   frame-relay intf-type dce
   frame-relay route 102 interface Serial0/1 201
  !
  interface Serial0/1
   description Link to R2
   no ip address
   encapsulation frame-relay
   serial restart-delay 0
   clock rate 64000
   no frame-relay inverse-arp
   frame-relay lmi-type ansi
   frame-relay intf-type dce
   frame-relay route 201 interface Serial0/0 102
   frame-relay route 203 interface Serial0/2 302
  !
  interface Serial0/2
   description Link to R3
   no ip address
   encapsulation frame-relay
   serial restart-delay 0
   clock rate 64000
   no frame-relay inverse-arp
   frame-relay lmi-type ansi
   frame-relay intf-type dce
   frame-relay route 302 interface Serial0/1 203
   frame-relay route 304 interface Serial0/3 403
  !
  interface Serial0/3
   description Link to R4
   no ip address
   encapsulation frame-relay
   serial restart-delay 0
   clock rate 64000
   no frame-relay inverse-arp
   frame-relay lmi-type ansi
   frame-relay intf-type dce
   frame-relay route 403 interface Serial0/2 304
  !

The most important line is the frame-relay route command on each of the serial interface command.
The syntax is listed on this link.  Here is the syntax of frame-relay route command:

"frame-relay route in-dlci interface out-interface-type out-interface-number out-dlci[voice-encap size]"

I would rephrase it as the following:

"frame-relay route source-dlci interface exit-interface-type mod/num destination-dlci"

The following are the frame-relay configuration from the remote routers with the proper DLCI.  Just a reminder, the connection is a point-to-point on frame relay.

Configuration from R1

!
interface Serial0/0
 description Link to Frame Relay Switch
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 no frame-relay inverse-arp
 frame-relay lmi-type ansi
!
interface Serial0/0.12 point-to-point
 ip address 10.1.1.1 255.255.255.252
 frame-relay interface-dlci 102
!

Configuration from R2

!
interface Serial0/0
 description Link to Frame Relay Switch
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 no frame-relay inverse-arp
 frame-relay lmi-type ansi
!
interface Serial0/0.12 point-to-point
 ip address 10.1.1.2 255.255.255.252
 frame-relay interface-dlci 201
!

interface Serial0/0.23 point-to-point
 ip address 10.1.1.5 255.255.255.252
 frame-relay interface-dlci 203
!

Configuration from R3

!
interface Serial0/0
 description Link to Frame Relay Switch
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 no frame-relay inverse-arp
 frame-relay lmi-type ansi
!
interface Serial0/0.23 point-to-point
 ip address 10.1.1.6 255.255.255.252
 frame-relay interface-dlci 302
!
interface Serial0/0.34 point-to-point
 ip address 10.1.1.9 255.255.255.252
 frame-relay interface-dlci 304
!

Configuration from R4

!
interface Serial0/0
 description Link to Frame Relay Switch
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 no frame-relay inverse-arp
 frame-relay lmi-type ansi
!
interface Serial0/0.34 point-to-point
 ip address 10.1.1.10 255.255.255.252
 frame-relay interface-dlci 403
!



Configuring Cisco Devices to Use a Syslog Server

Here are the configuration on Cisco Router to send logging information to Kiwi Syslog Server.

Informaiton:
Syslog server IP address: 192.168.1.200/24

On Cisco Router

Line 1. # config t
Line 2. # service timestamps log datetime msec localtime showtimezone
Line 3. # logging 192.168.1.200
Line 4. # logging trap 7
Line 5. # logging facility local 7
Line 6. # end
Line 7. # show logging

There are 7 options for line 4:
Emergency: 0
Alert: 1
Critical: 2
Error: 3
Warning: 4
Notice: 5
Infomational: 6
Debug: 7

Use the level 7 with caution, because it can generate a large amount of syslog traffic in a busy network.