Autosave: 2025-03-14 17:01:58

neuron/7aecb0c4-f9f9-4579-9564-8a4cb5e9c958/SSH.md

@@ -0,0 +1,77 @@
+---
+tags: [encryption, shell, server-management]
+created: Tuesday, March 04, 2025
+---
+
+# SSH
+
+SSH is the de facto standard for remote access to a Unix machine.
+
+`ssh` is the client which you use to connect to another machine.
+
+`sshd` is the server that manages incoming client requests for access.
+
+## sshd
+
+Typically the SSH server will be turned off.
+
+To run at boot:
+
+```sh
+sudo systemctl enable sshd
+```
+
+To start immediately:
+
+```sh
+sudo systemctl start sshd
+```
+
+The `sshd` configuration is found in the directory `/etc/ssh`.
+
+The config file is `/etc/ssh/sshd_config`.
+
+Mostly you can leave this alone but the following is a useful property to set:
+
+```
+PermitRootLogin no
+```
+
+See [Disable non-root ssh access](Disable_non-root_ssh_access.md) for more.
+
+## Known hosts
+
+Within your home directory at `./ssh/known_hosts` you will find a record of all
+the public keys of the servers you have connected. This file exists for both
+servers and clients, e.g:
+
+```sh
+cat ./ssh/known_hosts
+# systemsobscure.net ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKn6vyv9b+Nk5r
+# YVSAk5KvsTiC24K6uSpzCHzgLNoqt2
+```
+
+This shows the public key of my server at `systemsobscure.net` along with
+others.
+
+## Authorized keys
+
+On servers only, there is also an `authorized_keys` file which shows the
+server's own public keys that it presents to clients.
+
+If I go to my server I see that this key matches the one I have on my client
+computer `known_hosts`:
+
+```sh
+sudo cat /etc/ssh/ssh_host_ed25519_key.pub
+# ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKn6vyv9b+Nk5rYVSAk5KvsTiC24K6uSpzCHzgLNoqt2 root@self-host-server
+
+```
+
+Each user on a server will also have a `~/.ssh` directory also containing an
+`authorized_keys` file. This contains the public keys of clients who are allowed
+to connect to that user account.
+
+Hence I see the same public key of my desktop client machine in both places.
+
+## How the tunnel is created

neuron/7aecb0c4-f9f9-4579-9564-8a4cb5e9c958/USB protocols and connectors.md

@@ -0,0 +1,28 @@
+---
+tags: [protocols, USB]
+created: Wednesday, March 12, 2025
+---
+
+# USB protocols and connectors
+
+Different USB connectors can transfer according to different protocols. A
+connector is not always tied to a specific protocol. For instance each
+subsequent generation of connector is typically backwards-compatible with the
+protocol of the connector that it superseded.
+
+Some connectors are limited to slower protocols but they have the example of
+being small which is a benefit for smaller devices. The USB-C connector is so
+good because it is both small and capable of supporting the most advanced
+protocols (USB-4 and Thunderbolt).
+
+The main types of USB connector:
+
+- USB-A/USB-B
+- USB-A/USB-B
+- Micro-USB ()
+- Mini-USB
+- USB-C
+
+The illustration below matches connector to the protocol supported:
+
+![](static/usb-illustration.png)

neuron/7aecb0c4-f9f9-4579-9564-8a4cb5e9c958/USB-C.md

@@ -0,0 +1,37 @@
+---
+tags: [hardware, usb]
+created: Wednesday, March 12, 2025
+---
+
+# USB-C
+
+The "C" in the name refers to the shape of the _connector_ not the protocol that
+is used for the data transfer. (This is the case for all USB "types" which makes
+things confusing.)
+
+Multiple protocols can use the same connector for input/output. For instance
+Thunderbolt can transfer over USB-C but not every port that can fit a USB-C is a
+Thunderbolt port. The device's internal hardware determines the protocols
+available.
+
+The USB-C connector can serve all of the following protocols (from slowest to
+fastest):
+
+- USB 1.0 (12mb/s)
+- USB 2.0 (480Mb/s)
+- USB 3.0 (5Gb/s)
+- USB 3.1 (10Gb/s)
+- USB 3.2 (20Gb/s)
+- USB 4 (40Gb/s)
+- Thunderbolt (40Gb/s)
+
+A USB-C connector is equipped to just charge a device as well as transfer data.
+
+The world is converging (often due to legislation) on USB-C as the global
+standard. It can be one connector for all existing protocols and future
+protocols (for about 15 years). Its physical design an form factor can support
+future advancements whilst using the same connector.
+
+Ultimately USB-C will be surpassed by more another yet more advanced connector
+and associated protocols but for the time being we can stop using the older
+models.

neuron/7aecb0c4-f9f9-4579-9564-8a4cb5e9c958/index.md

@@ -13,12 +13,16 @@ computer science.
 
 <a href="https://thomasabishop.github.io/eolas/tags">View tags</a>
  
-**Build ID:** 5607f042-29e2-4baf-8022-e34dadc3ad0f
+**Build ID:** 7aecb0c4-f9f9-4579-9564-8a4cb5e9c958
 
-**Published:** Sun 02 Mar 2025 15:06:38
+**Published:** Fri 14 Mar 2025 17:01:53
 
 ### Recent edits 
 
+- [[USB-C]] 
+- [[USB protocols and connectors]] 
+- [[SSH]] 
+- [[lsof]] 
 - [[a0ab0bfb_network_layer_clarification]] 
 - [[b01fd836_Transport_Layer_clarification]] 
 - [[Transport_Layer_of_Internet_Protocol]] 
@@ -35,13 +39,9 @@ computer science.
 - [[Setup encrypted harddrive]] 
 - [[Disk_size_utilities]] 
 - [[Let's_Encrypt]] 
-- [[Certificate_authorities]] 
-- [[Bash_colour_output]] 
-- [[e383b8b3_nginx_vs_traefik]] 
-- [[Proxies]] 
 
 
-### All notes (537) 
+### All notes (541) 
 
 - [[0716531c_rewilding_the_internet]] 
 - [[241fe1a3_the_Web_versus_modem_BBSs]] 
@@ -444,6 +444,7 @@ computer science.
 - [[S3]] 
 - [[SAM]] 
 - [[SQLite]] 
+- [[SSH]] 
 - [[Save_readonly_Vim_file]] 
 - [[Schema_Definition_Language_in_GraphQL]] 
 - [[Secrets_or_env_vars_in_AWS]] 
@@ -509,6 +510,8 @@ computer science.
 - [[Type_hinting]] 
 - [[Typing_built_in_React_hooks]] 
 - [[UFW_firewall_management]] 
+- [[USB protocols and connectors]] 
+- [[USB-C]] 
 - [[Union_types_in_TS]] 
 - [[Unknown_type_in_TS]] 
 - [[Update_a_Mongo_document]] 
@@ -573,6 +576,7 @@ computer science.
 - [[http_in_Node]] 
 - [[journald]] 
 - [[jq]] 
+- [[lsof]] 
 - [[ps]] 
 - [[python_advent_learnings]] 
 - [[systemd]] 

neuron/7aecb0c4-f9f9-4579-9564-8a4cb5e9c958/lsof.md

@@ -0,0 +1,65 @@
+---
+tags: [shell, procedural]
+created: Tuesday, March 04, 2025
+---
+
+# lsof
+
+`lsof` stands for _list open files_. It lists opened files and the processes
+using them.
+
+## Directory
+
+```sh
+lsof /home/thomas
+```
+
+```
+COMMAND    PID   USER  FD   TYPE DEVICE SIZE/OFF    NODE NAME
+pipewire  1025 thomas cwd    DIR  253,0     4096 7340035 /home/thomas
+wireplumb 1026 thomas cwd    DIR  253,0     4096 7340035 /home/thomas
+```
+
+## Pass in a pid
+
+```sh
+lsof -p 1175
+```
+
+```
+COMMAND    PID   USER  FD      TYPE             DEVICE SIZE/OFF    NODE NAME
+at-spi-bu 1175 thomas cwd       DIR              253,0     4096 7340035 /home/thomas
+at-spi-bu 1175 thomas rtd       DIR              259,2     4096       2 /
+at-spi-bu 1175 thomas txt       REG              259,2    26760 1225154 /usr/lib/at-spi-bus-launcher
+```
+
+## Networking
+
+### List programs using or listening to ports
+
+```sh
+lsof -i
+```
+
+```
+COMMAND    PID   USER  FD   TYPE DEVICE SIZE/OFF NODE NAME
+signal-de 3250 thomas  39u  IPv4 149863      0t0  TCP archlinux:44304->ac88393aca5853df7.awsglobalaccelerator.com:https (ESTABLISHED)
+slack     3602 thomas  18u  IPv4 138442      0t0  TCP archlinux:57950->ec2-18-169-55-40.eu-west-2.compute.amazonaws.com:https (ESTABLISHED)
+firefox   6177 thomas 147u  IPv4 138842      0t0  TCP archlinux:cresco-control->93.243.107.34.bc.googleusercontent.com:https (ESTABLISHED)
+```
+
+### Filter by specific port
+
+```sh
+lsof -i:22
+lsof -i4:22 # limit to IPv4 addresses
+
+```
+
+```
+COMMAND    PID   USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
+sshd     45448   root    3u  IPv4  640237      0t0  TCP *:ssh (LISTEN)
+sshd     45448   root    4u  IPv6  640239      0t0  TCP *:ssh (LISTEN)
+sshd    185660   root    4u  IPv4 2554538      0t0  TCP static.18.113.203.116.clients.your-server.de:ssh->0542cb12.skybroadband.com:57744 (ESTABLISHED)
+
+```

neuron/7aecb0c4-f9f9-4579-9564-8a4cb5e9c958/tags.md

@@ -4,7 +4,7 @@ unlisted: true
 ---
 
 # Tags
-[algebra](./tags#algebra), [algorithms](./tags#algorithms), [analogue](./tags#analogue), [android](./tags#android), [APIs](./tags#APIs), [arch-linux](./tags#arch-linux), [arithmetic](./tags#arithmetic), [ARPA](./tags#ARPA), [ARPANET](./tags#ARPANET), [awk](./tags#awk), [AWS](./tags#AWS), [aws-lambda](./tags#aws-lambda), [binary](./tags#binary), [bulletin-boards](./tags#bulletin-boards), [bus](./tags#bus), [C](./tags#C), [computer-architecture](./tags#computer-architecture), [computer-history](./tags#computer-history), [containerization](./tags#containerization), [CPU](./tags#CPU), [cryptography](./tags#cryptography), [csv](./tags#csv), [data-structures](./tags#data-structures), [data-types](./tags#data-types), [databases](./tags#databases), [design-patterns](./tags#design-patterns), [disks](./tags#disks), [docker](./tags#docker), [dynamodb](./tags#dynamodb), [ecopolsoc](./tags#ecopolsoc), [electricity](./tags#electricity), [electromagnetism](./tags#electromagnetism), [electronics](./tags#electronics), [encryption](./tags#encryption), [exponents](./tags#exponents), [file-system](./tags#file-system), [firewalls](./tags#firewalls), [fleeting](./tags#fleeting), [fractions](./tags#fractions), [git](./tags#git), [graphql](./tags#graphql), [hardware](./tags#hardware), [IaC](./tags#IaC), [internet](./tags#internet), [javascript](./tags#javascript), [jest](./tags#jest), [json](./tags#json), [JSON](./tags#JSON), [kernel](./tags#kernel), [Linux](./tags#Linux), [linux](./tags#linux), [literature](./tags#literature), [logic](./tags#logic), [logic-gates](./tags#logic-gates), [memory](./tags#memory), [Microsoft](./tags#Microsoft), [middleware](./tags#middleware), [modems](./tags#modems), [mongo-db](./tags#mongo-db), [mongoose](./tags#mongoose), [nand-to-tetris](./tags#nand-to-tetris), [network-protocols](./tags#network-protocols), [networks](./tags#networks), [node-js](./tags#node-js), [number-systems](./tags#number-systems), [number-theory](./tags#number-theory), [OOP](./tags#OOP), [operating-systems](./tags#operating-systems), [packet-switching](./tags#packet-switching), [physics](./tags#physics), [ports](./tags#ports), [prealgebra](./tags#prealgebra), [privacy](./tags#privacy), [procedural](./tags#procedural), [propositional-logic](./tags#propositional-logic), [proxies](./tags#proxies), [python](./tags#python), [question](./tags#question), [raspberry-pi](./tags#raspberry-pi), [react](./tags#react), [recursion](./tags#recursion), [regex](./tags#regex), [REST](./tags#REST), [S3](./tags#S3), [server-management](./tags#server-management), [set-theory](./tags#set-theory), [shell](./tags#shell), [SNS](./tags#SNS), [sound](./tags#sound), [SQL](./tags#SQL), [SQLite](./tags#SQLite), [SQS](./tags#SQS), [ssh](./tags#ssh), [storage](./tags#storage), [surveillance-capitalism](./tags#surveillance-capitalism), [systemd](./tags#systemd), [systems-programming](./tags#systems-programming), [testing](./tags#testing), [theorems](./tags#theorems), [theory-of-computation](./tags#theory-of-computation), [time](./tags#time), [TOR](./tags#TOR), [Turing](./tags#Turing), [typescript](./tags#typescript), [unix](./tags#unix), [VPN](./tags#VPN), [world-wide-web](./tags#world-wide-web), [yaml](./tags#yaml), 
+[algebra](./tags#algebra), [algorithms](./tags#algorithms), [analogue](./tags#analogue), [android](./tags#android), [APIs](./tags#APIs), [arch-linux](./tags#arch-linux), [arithmetic](./tags#arithmetic), [ARPA](./tags#ARPA), [ARPANET](./tags#ARPANET), [awk](./tags#awk), [AWS](./tags#AWS), [aws-lambda](./tags#aws-lambda), [binary](./tags#binary), [bulletin-boards](./tags#bulletin-boards), [bus](./tags#bus), [C](./tags#C), [computer-architecture](./tags#computer-architecture), [computer-history](./tags#computer-history), [containerization](./tags#containerization), [CPU](./tags#CPU), [cryptography](./tags#cryptography), [csv](./tags#csv), [data-structures](./tags#data-structures), [data-types](./tags#data-types), [databases](./tags#databases), [design-patterns](./tags#design-patterns), [disks](./tags#disks), [docker](./tags#docker), [dynamodb](./tags#dynamodb), [ecopolsoc](./tags#ecopolsoc), [electricity](./tags#electricity), [electromagnetism](./tags#electromagnetism), [electronics](./tags#electronics), [encryption](./tags#encryption), [exponents](./tags#exponents), [file-system](./tags#file-system), [firewalls](./tags#firewalls), [fleeting](./tags#fleeting), [fractions](./tags#fractions), [git](./tags#git), [graphql](./tags#graphql), [hardware](./tags#hardware), [IaC](./tags#IaC), [internet](./tags#internet), [javascript](./tags#javascript), [jest](./tags#jest), [json](./tags#json), [JSON](./tags#JSON), [kernel](./tags#kernel), [Linux](./tags#Linux), [linux](./tags#linux), [literature](./tags#literature), [logic](./tags#logic), [logic-gates](./tags#logic-gates), [memory](./tags#memory), [Microsoft](./tags#Microsoft), [middleware](./tags#middleware), [modems](./tags#modems), [mongo-db](./tags#mongo-db), [mongoose](./tags#mongoose), [nand-to-tetris](./tags#nand-to-tetris), [network-protocols](./tags#network-protocols), [networks](./tags#networks), [node-js](./tags#node-js), [number-systems](./tags#number-systems), [number-theory](./tags#number-theory), [OOP](./tags#OOP), [operating-systems](./tags#operating-systems), [packet-switching](./tags#packet-switching), [physics](./tags#physics), [ports](./tags#ports), [prealgebra](./tags#prealgebra), [privacy](./tags#privacy), [procedural](./tags#procedural), [propositional-logic](./tags#propositional-logic), [protocols](./tags#protocols), [proxies](./tags#proxies), [python](./tags#python), [question](./tags#question), [raspberry-pi](./tags#raspberry-pi), [react](./tags#react), [recursion](./tags#recursion), [regex](./tags#regex), [REST](./tags#REST), [S3](./tags#S3), [server-management](./tags#server-management), [set-theory](./tags#set-theory), [shell](./tags#shell), [SNS](./tags#SNS), [sound](./tags#sound), [SQL](./tags#SQL), [SQLite](./tags#SQLite), [SQS](./tags#SQS), [ssh](./tags#ssh), [storage](./tags#storage), [surveillance-capitalism](./tags#surveillance-capitalism), [systemd](./tags#systemd), [systems-programming](./tags#systems-programming), [testing](./tags#testing), [theorems](./tags#theorems), [theory-of-computation](./tags#theory-of-computation), [time](./tags#time), [TOR](./tags#TOR), [Turing](./tags#Turing), [typescript](./tags#typescript), [unix](./tags#unix), [USB](./tags#USB), [usb](./tags#usb), [VPN](./tags#VPN), [world-wide-web](./tags#world-wide-web), [yaml](./tags#yaml), 
 
 ### algebra 
 
@@ -371,6 +371,7 @@ unlisted: true
 - [[HTTPS]] 
 - [[Let's_Encrypt]] 
 - [[Setup encrypted harddrive]] 
+- [[SSH]] 
 - [[What_can_the_ISP_see]] 
 ### exponents 
 
@@ -440,6 +441,7 @@ unlisted: true
 - [[Machine_code]] 
 - [[Motherboard]] 
 - [[Network_card]] 
+- [[USB-C]] 
 ### IaC 
 
 - [[Terraform]] 
@@ -865,6 +867,7 @@ unlisted: true
 - [[Killing_processes]] 
 - [[LineageOS_backup]] 
 - [[Linux_disk_partitions]] 
+- [[lsof]] 
 - [[Monitor_DNS_resolution_and_internet_connectivity_script]] 
 - [[Monitoring_processes_and_resources]] 
 - [[Network_packet_analysis_tools]] 
@@ -919,6 +922,9 @@ unlisted: true
 - [[Truth_tables]] 
 - [[Truth_trees]] 
 - [[Validity_and_entailment]] 
+### protocols 
+
+- [[USB protocols and connectors]] 
 ### proxies 
 
 - [[e383b8b3_nginx_vs_traefik]] 
@@ -1033,6 +1039,7 @@ unlisted: true
 - [[Firewalls]] 
 - [[HTTPS]] 
 - [[Let's_Encrypt]] 
+- [[SSH]] 
 - [[UFW_firewall_management]] 
 ### set-theory 
 
@@ -1068,6 +1075,7 @@ unlisted: true
 - [[Listing_and_navigating_directories_in_the_Shell]] 
 - [[Lists_and_arrays_in_Bash]] 
 - [[Loops_in_bash]] 
+- [[lsof]] 
 - [[Passing_arguments_and_options_to_Bash_scripts]] 
 - [[Proper_shebang_syntax]] 
 - [[ps]] 
@@ -1077,6 +1085,7 @@ unlisted: true
 - [[Redirection_in_Bash]] 
 - [[Shell_sessions]] 
 - [[Split_into_array_in_Bash]] 
+- [[SSH]] 
 - [[Strings_in_Bash]] 
 - [[Substrings_in_Bash]] 
 - [[Symlinks]] 
@@ -1212,6 +1221,12 @@ unlisted: true
 ### unix 
 
 - [[Time_and_computers]] 
+### USB 
+
+- [[USB protocols and connectors]] 
+### usb 
+
+- [[USB-C]] 
 ### VPN 
 
 - [[How_tunneling_works_with_VPNs]] 

zk/SSH.md

@@ -0,0 +1,77 @@
+---
+tags: [encryption, shell, server-management]
+created: Tuesday, March 04, 2025
+---
+
+# SSH
+
+SSH is the de facto standard for remote access to a Unix machine.
+
+`ssh` is the client which you use to connect to another machine.
+
+`sshd` is the server that manages incoming client requests for access.
+
+## sshd
+
+Typically the SSH server will be turned off.
+
+To run at boot:
+
+```sh
+sudo systemctl enable sshd
+```
+
+To start immediately:
+
+```sh
+sudo systemctl start sshd
+```
+
+The `sshd` configuration is found in the directory `/etc/ssh`.
+
+The config file is `/etc/ssh/sshd_config`.
+
+Mostly you can leave this alone but the following is a useful property to set:
+
+```
+PermitRootLogin no
+```
+
+See [Disable non-root ssh access](./Disable_non-root_ssh_access.md) for more.
+
+## Known hosts
+
+Within your home directory at `./ssh/known_hosts` you will find a record of all
+the public keys of the servers you have connected. This file exists for both
+servers and clients, e.g:
+
+```sh
+cat ./ssh/known_hosts
+# systemsobscure.net ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKn6vyv9b+Nk5r
+# YVSAk5KvsTiC24K6uSpzCHzgLNoqt2
+```
+
+This shows the public key of my server at `systemsobscure.net` along with
+others.
+
+## Authorized keys
+
+On servers only, there is also an `authorized_keys` file which shows the
+server's own public keys that it presents to clients.
+
+If I go to my server I see that this key matches the one I have on my client
+computer `known_hosts`:
+
+```sh
+sudo cat /etc/ssh/ssh_host_ed25519_key.pub
+# ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKn6vyv9b+Nk5rYVSAk5KvsTiC24K6uSpzCHzgLNoqt2 root@self-host-server
+
+```
+
+Each user on a server will also have a `~/.ssh` directory also containing an
+`authorized_keys` file. This contains the public keys of clients who are allowed
+to connect to that user account.
+
+Hence I see the same public key of my desktop client machine in both places.
+
+## How the tunnel is created

zk/USB protocols and connectors.md

@@ -0,0 +1,28 @@
+---
+tags: [protocols, USB]
+created: Wednesday, March 12, 2025
+---
+
+# USB protocols and connectors
+
+Different USB connectors can transfer according to different protocols. A
+connector is not always tied to a specific protocol. For instance each
+subsequent generation of connector is typically backwards-compatible with the
+protocol of the connector that it superseded.
+
+Some connectors are limited to slower protocols but they have the example of
+being small which is a benefit for smaller devices. The USB-C connector is so
+good because it is both small and capable of supporting the most advanced
+protocols (USB-4 and Thunderbolt).
+
+The main types of USB connector:
+
+- USB-A/USB-B
+- USB-A/USB-B
+- Micro-USB ()
+- Mini-USB
+- USB-C
+
+The illustration below matches connector to the protocol supported:
+
+![](../img/usb-illustration.png)

zk/USB-C.md

@@ -0,0 +1,37 @@
+---
+tags: [hardware, usb]
+created: Wednesday, March 12, 2025
+---
+
+# USB-C
+
+The "C" in the name refers to the shape of the _connector_ not the protocol that
+is used for the data transfer. (This is the case for all USB "types" which makes
+things confusing.)
+
+Multiple protocols can use the same connector for input/output. For instance
+Thunderbolt can transfer over USB-C but not every port that can fit a USB-C is a
+Thunderbolt port. The device's internal hardware determines the protocols
+available.
+
+The USB-C connector can serve all of the following protocols (from slowest to
+fastest):
+
+- USB 1.0 (12mb/s)
+- USB 2.0 (480Mb/s)
+- USB 3.0 (5Gb/s)
+- USB 3.1 (10Gb/s)
+- USB 3.2 (20Gb/s)
+- USB 4 (40Gb/s)
+- Thunderbolt (40Gb/s)
+
+A USB-C connector is equipped to just charge a device as well as transfer data.
+
+The world is converging (often due to legislation) on USB-C as the global
+standard. It can be one connector for all existing protocols and future
+protocols (for about 15 years). Its physical design an form factor can support
+future advancements whilst using the same connector.
+
+Ultimately USB-C will be surpassed by more another yet more advanced connector
+and associated protocols but for the time being we can stop using the older
+models.

zk/lsof.md

@@ -0,0 +1,65 @@
+---
+tags: [shell, procedural]
+created: Tuesday, March 04, 2025
+---
+
+# lsof
+
+`lsof` stands for _list open files_. It lists opened files and the processes
+using them.
+
+## Directory
+
+```sh
+lsof /home/thomas
+```
+
+```
+COMMAND    PID   USER  FD   TYPE DEVICE SIZE/OFF    NODE NAME
+pipewire  1025 thomas cwd    DIR  253,0     4096 7340035 /home/thomas
+wireplumb 1026 thomas cwd    DIR  253,0     4096 7340035 /home/thomas
+```
+
+## Pass in a pid
+
+```sh
+lsof -p 1175
+```
+
+```
+COMMAND    PID   USER  FD      TYPE             DEVICE SIZE/OFF    NODE NAME
+at-spi-bu 1175 thomas cwd       DIR              253,0     4096 7340035 /home/thomas
+at-spi-bu 1175 thomas rtd       DIR              259,2     4096       2 /
+at-spi-bu 1175 thomas txt       REG              259,2    26760 1225154 /usr/lib/at-spi-bus-launcher
+```
+
+## Networking
+
+### List programs using or listening to ports
+
+```sh
+lsof -i
+```
+
+```
+COMMAND    PID   USER  FD   TYPE DEVICE SIZE/OFF NODE NAME
+signal-de 3250 thomas  39u  IPv4 149863      0t0  TCP archlinux:44304->ac88393aca5853df7.awsglobalaccelerator.com:https (ESTABLISHED)
+slack     3602 thomas  18u  IPv4 138442      0t0  TCP archlinux:57950->ec2-18-169-55-40.eu-west-2.compute.amazonaws.com:https (ESTABLISHED)
+firefox   6177 thomas 147u  IPv4 138842      0t0  TCP archlinux:cresco-control->93.243.107.34.bc.googleusercontent.com:https (ESTABLISHED)
+```
+
+### Filter by specific port
+
+```sh
+lsof -i:22
+lsof -i4:22 # limit to IPv4 addresses
+
+```
+
+```
+COMMAND    PID   USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
+sshd     45448   root    3u  IPv4  640237      0t0  TCP *:ssh (LISTEN)
+sshd     45448   root    4u  IPv6  640239      0t0  TCP *:ssh (LISTEN)
+sshd    185660   root    4u  IPv4 2554538      0t0  TCP static.18.113.203.116.clients.your-server.de:ssh->0542cb12.skybroadband.com:57744 (ESTABLISHED)
+
+```