Git: Create a branch on your local machine, switch to it and then push it on the server

Following are a couple of simple commands that we use daily to create a new branch on git and push it to the git server.

The following command will create locally a new branch called branch_name and switch to it.

git checkout -b branch_name;

The following command will push the local branch you are currently switched to on the git server.
It will be made available to the server using the name branch_name.

git push --set-upstream origin branch_name;

How to find the program interpreter that a Linux application requests 1

Recently we tried to execute an application and we got the following error:
-bash: ./main: No such file or directory
This error occurred because our application was trying to use an interpreter that was not available on that machine.
We used the readelf utility that displays information about ELF files (including the interpreter information) to resolve our issue.
Specifically we used readelf -l ./main which displays the information contained in the file’s segment headers, if it has any.
(You can replace the parameter -l with --program-headers or --segments, they are the same).

From the data that was produced we only needed the following line:

[Requesting program interpreter: /lib/ld-linux-armhf.so.3]
so we used grep to filter out all other lines and then cut and tr to get the data after the : character (second column) and then remove all spaces and the ] character from the result.
The full and final command we used was:
readelf -l ./main | grep 'Requesting' | cut -d':' -f2 | tr -d ' ]';

Device has MAC address X, instead of configured address Y.

Recently, we tried to take a network interface down on a VM, when we executed the command

ifdown eth0

we got the following error:

ERROR    : [/etc/sysconfig/network-scripts/ifdown-eth] Device  has MAC address 00:00:00:00:00:00
 00:45:4D:04:02:36
 00:45:4D:04:02:40, instead of configured address 00:45:4D:16:0B:29. Ignoring.

We used ifconfig eth0 to check the information on the network interfaces which resulted in the following data:

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
 inet 10.1.20.115  netmask 255.255.255.0  broadcast 10.1.20.255
 inet6 fe80::215:5dff:fe01:236  prefixlen 64  scopeid 0x20<link>
 ether 00:45:4d:04:02:36  txqueuelen 1000  (Ethernet)
 RX packets 10103919  bytes 5474528935 (5.0 GiB)
 RX errors 0  dropped 0  overruns 0  frame 0
 TX packets 6541413  bytes 1190276207 (1.1 GiB)
 TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

We saw that the value ether for eth0 was 00:45:4d:04:02:36, which was one of the addresses the warning mentioned that are valid.

Apparently, we had an error in the following configuration file:

/etc/sysconfig/network-scripts/ifcfg-eth0

The value for HWADDR was set to 00:45:4D:16:0B:29 which was wrong (most likely this file was copied here from another source), after we updated the value to 00:45:4d:04:02:36 we were able to use the device normally.

Fedora: Start a Virtual Machine using a physical hard disk

Recently, we wanted to start a Virtual Machine running a Windows installation from a physical hard disk.

We could not find a way for GNOME Boxes to achieve this, so we installed qemu to do so.

We installed qemu using:


sudo dnf install qemu -y;

Configuring our command to start the Virtual Machine from the physical hard drive:

  • Our hard disk was identified on the physical machine as /dev/sda so we set the -hda parameter to that value.
  • Then we added the parameter -boot c to instruct the virtual machine to boot from the first hard disk.
  • The default guest start-up RAM size was 128 MiB, so we set the parameter -m to 4096 to give to the virtual machine 4GB of RAM.
  • Finally we added the -snapshot parameter which instructed the system to write to temporary files instead of the disk image files (all disk images are considered as read only).
    In this case, the raw disk image used are not written back. When sectors are written, they are written in a temporary file created in /tmp.
    You can however force the write back to the raw disk images by using the commit monitor command (or C-a s in the serial console).

In the end our command was as follows:


sudo qemu-kvm -snapshot -m 4096 -boot c -hda /dev/sda;