NerdOfLinux's questions

When I run either of the following in the terminal:

''

""

I get the following output:

Command '' not found, but can be installed with:

sudo apt install libpam-mount      
sudo apt install openssh-server    
sudo apt install openvswitch-common
sudo apt install openvswitch-switch
sudo apt install php-common        
sudo apt install bpfcc-tools       
sudo apt install mailutils-mh      
sudo apt install mmh               
sudo apt install nmh 

But, when I just press enter, nothing happens. Shouldn't these two cases have the same output of nothing?

I'm running a headless device that I want to connect to wifi(it's currently on ethernet), so I'm using nmcli. I scan for connections with the following:

sudo nmcli dev wifi rescan
sudo nmcli dev wifi list

and the WiFi network I want is at 95% strength. So, I connect with:

sudo nmcli dev wifi connect "SSID" password "wifipassword"

and I get the following error:

Error: Connection activation failed: (53) The Wi-Fi network could not be found.

and I've tried copying and pasting from list to ensure I did not mistype the SSID, and it still does not work. It works fine from other devices that use Ubuntu and network-manager, so I know it's not the router.

How can it not find the network when I connect, but find it just fine when scanning, and how do I fix this?

In the terminal, one way to reference home is by using ~/. I don't understand how this works, because the output of file ~/ is:

/home/admin/: directory

and just running ~/ results in:

-bash: /home/admin/: Is a directory

so what's converting ~/ into /home/admin?

~/ also appears to work in /bin/dash, so I also know it's not bash specific.

I've found conflicting information on the internet on whether the bs in a command like dd bs=512 if=/home/Downloads/ubuntu.iso of=/dev/sdb stands for "bytes per second" or "block size". I couldn't find anything in the man pages, as the only reference to bs is:

bs=BYTES

read and write up to BYTES bytes at a time

I'm wondering what the difference is between creating a swapfile with

fallocate -l 1G /swapfile

and

dd if=/dev/zero of=/swapfile bs=1024 count=1024

both seem to work fine, but does one have an advantage over the other?

The only thing I could find online was that fallocate does not work on all file systems.

On my VPS, when I run

ping 8.8.8.8

It works just fine, but when I do

ping google.com

it just hangs. The contents of /etc/resolv.conf is:

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by 
resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 108.61.10.10
nameserver 208.67.222.222
nameserver 208.67.220.220

and I know OpenDNS works fine. I think the problem is with iptables, because it was working fine before I changed the iptables settings iptables -S is:

-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-A INPUT -p tcp -m tcp -m multiport ! --dports 80,443,8080,2222,22,1194,993,25,995,143,110,4433 -j DROP
-A INPUT -p udp -m udp -m multiport ! --dports 53,1194,500,4500 -j DROP
-A INPUT -p tcp -m connlimit --connlimit-above 25 --connlimit-mask 32 --connlimit-saddr -j REJECT --reject-with tcp-reset
-A INPUT -p tcp -m tcp --tcp-flags RST RST -m limit --limit 2/sec --limit-burst 2 -j ACCEPT
-A INPUT -p tcp -m tcp --tcp-flags RST RST -j DROP
-A INPUT -p tcp -m conntrack --ctstate NEW -m limit --limit 20/sec --limit-burst 20 -j ACCEPT
-A INPUT -p tcp -m conntrack --ctstate NEW -j DROP

I have set up libpam-google-authenticator according to https://www.digitalocean.com/community/tutorials/how-to-set-up-multi-factor-authentication-for-ssh-on-ubuntu-16-04

It works, but the problem is that I can't log in with a password, it need to be with a key. If there is no key, I get permission denied public key without even being asked for a password. How can I get it to work with a public key + two factor OR password + two factor?

Fail2Ban works fine with the built-in jails, but my custom OpenVPN jail doesn't ban anything, neither does my NGINX-DoS jail. The output of sudo fail2ban-client status openvpn is:

Status for the jail: openvpn
|- Filter
|  |- Currently failed: 0
|  |- Total failed: 0
|  `- File list:    /var/log/openvpn.log
- Actions
|- Currently banned:    2
|- Total banned:    2
`- Banned IP list:  1.2.3.4 1.3.4.5

I changed the IP addresses, BTW. So the jail is working, but the output of iptables-save | grep 1.2.3.4 returns nothing, so the IP is not being blocked. All other jails work fine.

My openvpn.conf file in filter.d is:

# Fail2Ban filter for selected OpenVPN rejections
#
#
[INCLUDES]

before = common.conf

[Definition]

failregex = ^ TLS Error: incoming packet authentication failed from \
[AF_INET\]<HOST>:\d+$
        ^ <HOST>:\d+ Connection reset, restarting
        ^ <HOST>:\d+ TLS Auth Error
        ^ <HOST>:\d+ TLS Error: TLS handshake failed$
        ^ <HOST>:\d+ VERIFY ERROR

ignoreregex = 

and the section in jail.local is:

[openvpn]
enabled  = true
port     = 1194
protocol = tcp
backend = auto
filter   = openvpn
logpath  = /var/log/openvpn.log
action = sendmail[name=openvpn, dest=my_email@my_domain.com]
banaction = iptables-multiport

The same thing is happening with my NGINX jail, fail2ban-client says its banned, and I get an email saying an IP was banned, but nothing happens.

If I type

::

into a bash shell, I get:

-bash: ::: command not found

But, only one : results in no output. Why is this?

Just for fun, on a VPS I was about to terminate anyway, I ran

sudo rm -rf / --no-preserve-root

and after that all commands, including

/bin/bash

returned command not found, which makes sense as they were deleted. But how was I still SSHed into it, and able to somewhat use bash even though the files no longer existed?

I understand that the load balance is a way of measuring how busy the CPU is. However, I don't understand how a load average of 0.00 can exist. Doesn't the kernel always run? Doesn't that take part of the CPU load?

What's the difference between:

ln -s /mnt/extra/home /

and

mkdir /home
mount --rbind /mnt/extra/home /home

In Python, when I run a command with

os.system

what shell gets used?

I have a single core VPS with a load average that goes beyond 25 at times. When it reaches that, it becomes unbearably slow, and even commands run through dash, which is faster and uses less RAM than bash, takes a while to run. How can I track down what process is causing the high load?

If the system doesn't have enough RAM for everything, does the kernel take the nice value into account when it decides what to swap out to reduce memory stress?

What happens if you run

sudo deluser root

will sudo still work, and will the system still work?

I have an encrypted file that is encoded with base64:

U2FsdGVkX19hoS7DQSHERIkTzT3Hp7RUEjMAh6UDOP6YjRB/XQey7TKoySJiZTni
WbCfJLhihMD9CkohBnvrY8UBkh2dbi1K6hQqf8X9ENGFNWUxqmhYMG+WrBsPwhpB
I1qUt91IKlPS1YMZ0UDyBieDwFyqFi3izGhqXoOuzo8=

and when I run:

cat encryptedfile | openssl enc -d -a

I get a bunch of question mark symbols. Why does that happen?

When my current 2TB RAID 1 array(with 2 disks) gets full, how can I add more storage? I'm aware that RAID 1 keeps both disks identical, and that I need to replace both. Basically, how can I change disks without losing all my data?

How can I keep an SSH connection alive without actively using it. When I use it, it works fine, but when I don't use it for a few minutes, it disconnects. As I get an email each time I connect, how can I keep the SSH session alive?

Note: In my .ssh/config file, at the top I have

Host *
ServerAliveInterval 3

but it doesn't seem to work.

I know you can't put a port in /etc/hosts, so how can I achieve the equivalent of:

127.0.0.1     https://website.com:4433

For WordPress, I need CURL to go to 127.0.0.1 on port 4433. As it's wordpress and not a script I made, I can't change that.