When you want to discover LAN metadata without being part of that network. So, when you want to discover network address range, gateway, DNS IPs, DHCP server IPs, etc. this simple nmap parameter will help you so much.
# nmap --script broadcast-dhcp-discover
Starting Nmap 7.60 ( https://nmap.org ) at 2021-05-19 15:07 CEST
Pre-scan script results:
| Response 1 of 1:
| IP Offered: 192.168.1.127
| DHCP Message Type: DHCPOFFER
| Subnet Mask: 255.255.255.0
| Renewal Time Value: 4d00h00m00s
| Rebinding Time Value: 7d00h00m00s
| IP Address Lease Time: 8d00h00m00s
| Server Identifier: 192.168.1.1
| Router: 192.168.1.1
|_ Domain Name Server: 188.8.131.52, 184.108.40.206
WARNING: No targets were specified, so 0 hosts scanned.
Nmap done: 0 IP addresses (0 hosts up) scanned in 1.43 seconds
Simple shell script based on bash which monitor a host with command line ping. Just bash and ping are the unique dependencies. Only state change are going to be printed:
echo "$(date '+%Y-%m-%dT%H:%M:%S') - " + $STATE;
ping -c 4 $IP > /dev/null 2>&1
if [ "$?" = "0" ]; then
if [ "$STATE" = "offline" ];
if [ "$STATE" = "online" ];
When you work with embedded systems sometimes you would feel happy to have a Linux box until you discover there are plenty of basic things that you don’t have available, the extreme of that could be the ‘ps’ command which is used most of the time for checking if any process is running . Maybe you know that thanks the /proc filesystem there is access to the source of the information.
Keep next command close for solving this inconvenience he next time:
I’m a byobu user for a long time, I love it for many reasons. But this is just a quick tip for extreme users like me. I mean people who use byobu for local consoles with remote byobu sessions running on top of SSH, for instance.
When prefix key combinations has to be sent to the remote host we have to press “Control + a + a” and finally the command that we want to send to the remote systems. This is not comfortable many times. So, I modified my configuration file for changing the prefix when I want to send remote commands to the nested byobu.
This is going to work this way:
Control + a
as a prefix for local byobu session.
Control + b
as a prefix for remote byobu session
Take a look on this screen capture where you can see byobu status bars stacked.
If you find useful the configuration that I described the only thing that you have to do is modify the configuration file: ~/.byobu/keybindings.tmux
unbind-key -n C-a
set -g prefix C-a
set -g prefix2 F12
unbind-key -n C-b
bind-key -n C-b send-prefix
Usually, simple things are the best, in the case I want to recommend an FTP server for Windows. This is a really simple but super useful FTP server for Windows. I’m using in Windows 10 and it works perfectly. Configuration is done in less than 10″ and installation is not required, I love that. Super portable.
Don’t expect sophisticated options but the most useful and advanced ones are there. If you need something like that my recommendation is:
I imagine you are used to using curl for many command line scripts, tests, and much more things. I did the same but some weeks ago I discovered HTTPie which is the best substitute that I’ve ever found for curl. Of course, it’s also available for a lot of Linux distributions, Windows, and Mac. But I used it with docker which is much more transparent for the operative system and easy to update. To be more precise I use next alias trick for using this tool:
alias http='sudo docker run -it --rm --net=host clue/httpie'
When we have a file with a ‘dd’ of a full disk and we want to mount a partition of that disk, we have to use an offset for jumping to the beginning of the partition that we want to mount.
Using ‘fdisk’ command we can find the partitions of that disk copied inside a file.
fdisk -l FILE_WITH_DISK_INSIDE
Once partition table is shown there is a column called ‘Start’ using the corresponding number in this column for the partition that we want we can obtain the offset required for our mounting point. Reasoning behind that is multiply start sector per number of bytes per sector.
# OFFSET = START * 512
mount -o ro,loop,offset=OFFSET FILE_WITH_DISK_INSIDE /mnt
I hope thanks to this technical note next time that I forget how to get the offset I find it fastly.
If you don’t want to do that manually, there is a small tool called losetup which maps the partitions of a disk image on a file.
# example, attaching partitions to loopback devices
losetup -P /dev/loop0 DISK_IMAGE
# just mount the devices now, they are /dev/loop0pX where X is the number of the partition
# dettach this assignament:
losetup -d /dev/loop0
Reading time: < 1 minute
This is another short entry, in this case for recommending a service which we solve typical problem solved using a DNAT. Once we have a service on our laptop, or on a private server and we have to expose that service on the internet for some time or permanently usually we have to go the firewall, or router and create a NAT rule forwarding a port. This is a simple and powerful service which is going to solve that for you.
There is a free account for understanding and testing the service, other plans are available and especially affordable for professional requirements.
This is going to be a very short post entry, I just want to refer a very interesting mail relay (smart host) which define itself like:
Email delivery services built for developers, by developers
Combined with your language of choice, using the power of our robust cloud API couldn’t be easier.
Open a SparkPost account today and send up to 100.000 emails per month for free. The best is you can do using SMTP or using a REST API; really nice easy to use an powerful control dashboard simplify externally keys management, statistics, templates for mailings, and many more features.
Personally I love the service because is extremely useful to be configured on SSMTP service of Linux as a default relay host, for personal and professional use. Another use could be to check end-to-end mail services.
Personally I love the service, and if you want to send really big mailings theirs costs are very competitive.