vault backup: 2025-03-20 11:07:48

57 files changed, 778 insertions, 6 deletions

diff --git a/3 Resources/Bash.md b/3 Resources/Bash.md
deleted file mode 100644
index 841443f..0000000
--- a/3 Resources/Bash.md
+++ /dev/null
@@ -1 +0,0 @@
-How to [[Reference arguments]].
\ No newline at end of file
diff --git a/3 Resources/Bash/Expansion.md b/3 Resources/Bash/Expansion.md
new file mode 100644
index 0000000..1cd3209
--- /dev/null
+++ b/3 Resources/Bash/Expansion.md
@@ -0,0 +1,9 @@
+---
+tags:
+  - bash
+---
+Find about in the manual `man bash` (search EXPANSION). This document will hold some often used expansions.
+
+**Variable expansion**
+substr
+`${VAR:offset:len}`
\ No newline at end of file
diff --git a/3 Resources/Bash/Generate random integers.md b/3 Resources/Bash/Generate random integers.md
new file mode 100644
index 0000000..8835716
--- /dev/null
+++ b/3 Resources/Bash/Generate random integers.md
@@ -0,0 +1,19 @@
+---
+tags:
+  - bash
+---
+The environment variable `RANDOM` contains an int between 0-32768.
+
+```
+min=10
+max=20 
+echo $(($RANDOM%($max-$min+1)+$min))
+20
+echo $(($RANDOM%($max-$min+1)+$min))
+14
+```
+
+Using parameter [[Expansion]] we can just grab the first number:
+```
+${RANDOM:0}
+```
\ No newline at end of file
diff --git a/3 Resources/Bash/Heredoc.md b/3 Resources/Bash/Heredoc.md
new file mode 100644
index 0000000..703e3e5
--- /dev/null
+++ b/3 Resources/Bash/Heredoc.md
@@ -0,0 +1,16 @@
+```
+read -r -d '' VAR <<EOF
+blaat
+EOF
+```
+
+```
+var=$(
+cat <<EOF
+blaat
+EOF
+)
+```
+
+Quote EOF/NAME to prevent expansion
+Put  - after << to remove indentation from result
\ No newline at end of file
diff --git a/3 Resources/Dictionary/Scalar type.md b/3 Resources/Dictionary/Scalar type.md
new file mode 100644
index 0000000..3cd22be
--- /dev/null
+++ b/3 Resources/Dictionary/Scalar type.md
@@ -0,0 +1,13 @@
+---
+tags:
+  - programming
+  - dictionary
+---
+A scalar type represents a single value. Thus
+- int
+- float
+- string
+- double 
+- boolean
+
+are all scalar types ( even though they can have a class such as in python or rust! ).
\ No newline at end of file
diff --git a/3 Resources/Dictionary/Type inference.md b/3 Resources/Dictionary/Type inference.md
new file mode 100644
index 0000000..7b8d8e1
--- /dev/null
+++ b/3 Resources/Dictionary/Type inference.md
@@ -0,0 +1,17 @@
+---
+tags:
+  - programming
+  - dictionary
+---
+This is when the compiler can infer (determine) the type of a variable by looking at the value being assigned.
+
+For example:
+```rust
+let x = 1
+
+# Equals
+
+let x: u32 = 1;
+```
+
+But the Rust compiler infers that x is u32 because that is the default int type.
\ No newline at end of file
diff --git a/3 Resources/Git/Edit existing commits.md b/3 Resources/Git/Edit existing commits.md
new file mode 100644
index 0000000..9832ee5
--- /dev/null
+++ b/3 Resources/Git/Edit existing commits.md
@@ -0,0 +1,22 @@
+---
+tags:
+  - git
+---
+I've found a nice and easy way to edit existing commits. Before I used the following "tedious" process.
+```
+git stash # Git rebase wants a clean working tree
+git rebase -i <main|master|whatever branch your branched off>
+... in the interactive editor, find the commit to edit, and mark it to edit ...
+... write & quit ...
+git stash pop # Optional. Only if you've already made the changes on HEAD.
+git commit --amend
+git rebase --continue
+```
+
+Now we can do something much easier using a so called "fixup commit".
+
+```
+git commit --fixup=<commit_id_to_fix>
+git rebase -i --autosquash <main|master|whatever branch you branched off>
+... write & quit
+```
\ No newline at end of file
diff --git a/3 Resources/Git/Find files in history.md b/3 Resources/Git/Find files in history.md
new file mode 100644
index 0000000..d5592fe
--- /dev/null
+++ b/3 Resources/Git/Find files in history.md
@@ -0,0 +1,17 @@
+---
+tags:
+  - git
+references:
+  - https://stackoverflow.com/questions/7203515/how-to-find-a-deleted-file-in-the-project-commit-history
+---
+Find a (deleted) file in all commits.
+`g lg --all --full-history -- "**/shell.nix"`
+or more generally
+`g lg --all --full-history -- <path-to-file>`
+then using the SHA
+`g show <sha> -- <path-to-file>`
+
+**Epic bonus**
+Restore the file:
+`g checkout <sha>^ -- <path-to-file>`
+the caret (`^`) references one commit before sha, because in sha it is deleted.
\ No newline at end of file
diff --git a/3 Resources/Index/Bash.md b/3 Resources/Index/Bash.md
new file mode 100644
index 0000000..cee90e3
--- /dev/null
+++ b/3 Resources/Index/Bash.md
@@ -0,0 +1,8 @@
+---
+tags:
+  - bash
+---
+* [[Reference arguments]].
+* [[Generate random integers]]
+* [[Expansion]]
+* [[Heredoc]]
\ No newline at end of file
diff --git a/3 Resources/Index/Nix.md b/3 Resources/Index/Nix.md
new file mode 100644
index 0000000..60a8e40
--- /dev/null
+++ b/3 Resources/Index/Nix.md
@@ -0,0 +1,8 @@
+---
+tags:
+  - nix
+  - index
+---
+[[Interpolation]]
+[[NixOS Modules]]
+[[Shell]]
\ No newline at end of file
diff --git a/3 Resources/Index/jq.md b/3 Resources/Index/jq.md
new file mode 100644
index 0000000..07d43aa
--- /dev/null
+++ b/3 Resources/Index/jq.md
@@ -0,0 +1,7 @@
+---
+tags:
+  - jq
+references:
+  - https://jqlang.org/
+---
+[[about]]
diff --git a/3 Resources/Linux/BatchMode.md b/3 Resources/Linux/BatchMode.md
new file mode 100644
index 0000000..e45de5a
--- /dev/null
+++ b/3 Resources/Linux/BatchMode.md
@@ -0,0 +1,6 @@
+---
+tags:
+  - ssh
+  - linux
+---
+With BatchMode if SSH will fail instantly if the key is rejected, rather than prompting for a password and causing scripts to hang indefinitely.
\ No newline at end of file
diff --git a/3 Resources/Linux/Create  bootable USB.md b/3 Resources/Linux/Create  bootable USB.md
new file mode 100644
index 0000000..a296677
--- /dev/null
+++ b/3 Resources/Linux/Create  bootable USB.md
@@ -0,0 +1,8 @@
+---
+tags:
+  - linux
+  - bootable
+---
+```
+sudo dd bs=4M conv=fsync oflag=direct status=progress if=linux.iso of=/dev/sda
+```
\ No newline at end of file
diff --git a/3 Resources/Linux/Device mapper.md b/3 Resources/Linux/Device mapper.md
index 059a0d1..27980ca 100644
--- a/3 Resources/Linux/Device mapper.md
+++ b/3 Resources/Linux/Device mapper.md
@@ -4,7 +4,6 @@
 Device mapper is a kernel driver to map physical block devices to virtual ones; this means that for example we can have many physical devices be represented by a single virtual one (linear mapping).
 
 How does it work?
-[[1 projects/Inwerken Mohammed/TODO]]
 What is its function in relation to multipath?
 
 Logical devices using device-mapper can be managed using `man 8 dmsetup`
diff --git a/3 Resources/Linux/Exit SSH control master connection.md b/3 Resources/Linux/Exit SSH control master connection.md
new file mode 100644
index 0000000..7054d9d
--- /dev/null
+++ b/3 Resources/Linux/Exit SSH control master connection.md
@@ -0,0 +1,6 @@
+---
+tags:
+  - ssh
+  - linux
+---
+To exit an existing session use `ssh -O exit <user>@<host>`
\ No newline at end of file
diff --git a/3 Resources/Linux/filesystems/Tmpfs.md b/3 Resources/Linux/FS/Tmpfs.md
index b8fe839..b8fe839 100644
--- a/3 Resources/Linux/filesystems/Tmpfs.md
+++ b/3 Resources/Linux/FS/Tmpfs.md
diff --git a/3 Resources/Linux/FS/Writeback cache.md b/3 Resources/Linux/FS/Writeback cache.md
new file mode 100644
index 0000000..03917bb
--- /dev/null
+++ b/3 Resources/Linux/FS/Writeback cache.md
@@ -0,0 +1,36 @@
+---
+tags:
+  - linux
+  - qemu
+  - filesystem
+references:
+  - https://avidandrew.com/understanding-disk-cache-writeback-ext4.html
+  - https://docs.kernel.org/admin-guide/sysctl/vm.html#dirty-expire-centisecs
+---
+normal: write() -> cache (multiple layers) -> disk
+
+# Physical server write cache
+![[physical_write_cache.png]] 
+
+Page cache -> RAM
+
+Journal -> ensures data is fully written before the transaction is considered complete.
+`commit` mount option -> flushes cache to disk every x seconds (configurable), ==default = 5.==
+`barrier` mount option -> enables the ordering of groups of writes, controller ensures writes before barrier are written before writes after barrier. ==Default = 1==
+
+`commit` + dirty_expire_centisecs [2] ~ automatic persisting of data.
+
+If we call `sync`, `fsync` or `fdatasync` ourselves our data is forced on-disk right away by the kernel, no need to wait for commit + dirty_expirty_centisecs.
+
+# VM Write cache
+ Guest has its own page cache
+ ![[vm_write_cache.png]]
+
+QEMU/KVM options for disk caches:
+- Writeback -> write complete if in host page cache; guest required to flush for integrity.
+- Writethrough -> write complete if committed to disk; guest no need to flush.
+- None -> Equivalent to direct access to host disk. Guest needs to flush.
+- Unsafe -> eq writeback but flush ignored. Performance.
+- Directsync -> writethrough but without host page cache.
+
+Safe if guest uses `commit` and `barrier` and therefore `fdatasync` syscalls on a recurring basis.
\ No newline at end of file
diff --git a/3 Resources/Linux/FS/physical_write_cache.png b/3 Resources/Linux/FS/physical_write_cache.png
new file mode 100644
index 0000000..819c834
--- /dev/null
+++ b/3 Resources/Linux/FS/physical_write_cache.png
diff --git a/3 Resources/Linux/FS/vm_write_cache.png b/3 Resources/Linux/FS/vm_write_cache.png
new file mode 100644
index 0000000..1c63843
--- /dev/null
+++ b/3 Resources/Linux/FS/vm_write_cache.png
diff --git a/3 Resources/Linux/Grepping stuff.md b/3 Resources/Linux/Grepping stuff.md
new file mode 100644
index 0000000..2d6af44
--- /dev/null
+++ b/3 Resources/Linux/Grepping stuff.md
@@ -0,0 +1,15 @@
+---
+tags:
+  - grep
+  - ripgrep
+  - linux
+---
+# Grep
+`grep -vxf gobs_servers onecrm_servers` grep all onecrm_servers that **ARE NOT** in gobs_servers
+`grep -oxf gobs_servers onecrm_servers` grep all onecrm_servers that **ARE** in gobs_servers
+`grep -vxf onecrm_servers gobs_servers` grep all gobs_servers that **ARE NOT** in onecrm_servers
+`grep -oxf onecrm_servers gobs_servers` grep all gobs_servers that **ARE** in onecrm_servers
+# Ripgrep
+Pass `-L` to `rg` to make it follow symlinks: this is handy for example when searching hieradata, because node definitions can be symlinked.
+
+	`-l` for showing only files with matches
\ No newline at end of file
diff --git a/3 Resources/Linux/NetworkManager.md b/3 Resources/Linux/NetworkManager.md
new file mode 100644
index 0000000..545124c
--- /dev/null
+++ b/3 Resources/Linux/NetworkManager.md
@@ -0,0 +1,43 @@
+---
+tags:
+  - linux
+  - networking
+references:
+  - https://networkmanager.dev/
+  - https://ubuntu.com/core/docs/networkmanager/configure-vpn
+  - https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/configuring_and_managing_networking/assembly_networkmanager-connection-profiles-in-keyfile-format_configuring-and-managing-networking
+---
+Connection profiles (nm-settings-nmcli(5))
+Networkmanager will only read profile files owned by root bc they often contain secrets.
+Keyfile format for connection profiles is .INI-like, but makes it possible for example to write a list of arrays in a space-seperated string?
+
+
+> Configuring secrets for when using OpenVPN together with NetworkManager in NixOS is complete dogshit. Avoid :) 
+
+Manually defining VPN
+https://networkmanager.dev/docs/api/latest/nm-settings-nmcli.html
+```
+nmcli c add connection.id vpntest connection.type vpn \
+    vpn.service-type org.freedesktop.NetworkManager.openvpn \
+    ipv4.never-default true \
+    ipv6.never-default true \
+    +vpn.data ca=/sjj:qvar/snap/network-manager/common/creds/server_ca.crt \
+    +vpn.data cert=/var/snap/network-manager/common/creds/user.crt \
+    +vpn.data cert-pass-flags=0 \
+    +vpn.data cipher=AES-128-CBC \
+    +vpn.data comp-lzo=adaptive \
+    +vpn.data connection-type=tls \
+    +vpn.data dev=tun \
+    +vpn.data key=/var/snap/network-manager/common/creds/user.key \
+    +vpn.data ping=10 \
+    +vpn.data ping-restart=60 \
+    +vpn.data remote=<server>:<port> \
+    +vpn.data remote-cert-tls=server \
+    +vpn.data ta=/var/snap/network-manager/common/creds/tls_auth.key \
+    +vpn.data ta-dir=1 \
+    +vpn.data verify-x509-name=name:access.is
+```
+
+
+Conver nmconnection into Nix
+https://github.com/janik-haag/nm2nix
\ No newline at end of file
diff --git a/3 Resources/Linux/Use type if which doesnt work.md b/3 Resources/Linux/Use type if which doesnt work.md
new file mode 100644
index 0000000..39881dc
--- /dev/null
+++ b/3 Resources/Linux/Use type if which doesnt work.md
@@ -0,0 +1,7 @@
+---
+tags:
+  - linux
+  - shell
+---
+Sometimes `which` will say: HEY it's a function!
+Then we can use `type` :) It even shows the defition!
\ No newline at end of file
diff --git a/3 Resources/Linux/Useful info about Debian packages.md b/3 Resources/Linux/Useful info about Debian packages.md
new file mode 100644
index 0000000..f401790
--- /dev/null
+++ b/3 Resources/Linux/Useful info about Debian packages.md
@@ -0,0 +1,9 @@
+---
+tags:
+  - debian
+  - packaging
+  - linux
+---
+https://www.debian.org/doc/debian-policy/index.html
+
+Specifically https://www.debian.org/doc/debian-policy/ch-relationships.html
\ No newline at end of file
diff --git a/3 Resources/Linux/Using GRUB we need an EF02 partition.md b/3 Resources/Linux/Using GRUB we need an EF02 partition.md
new file mode 100644
index 0000000..8fd3109
--- /dev/null
+++ b/3 Resources/Linux/Using GRUB we need an EF02 partition.md
@@ -0,0 +1,13 @@
+---
+tags:
+  - linux
+  - grub
+---
+I've learnt that to install GRUB we need an EF02 partition as the first partition.
+
+MBR -> first sector of disk contains boot loader
+GPT -> a seperate partition
+
+EF00 -> EFI System Partition (ESP)
+EF02 -> BIOS boot partition
+Both are partitions for GPT partitioned disks, just the type of firmware is different,.
\ No newline at end of file
diff --git a/3 Resources/math/Cartesian product.md b/3 Resources/Math/Cartesian product.md
index 161b405..161b405 100644
--- a/3 Resources/math/Cartesian product.md
+++ b/3 Resources/Math/Cartesian product.md
diff --git a/3 Resources/NFS.md b/3 Resources/NFS.md
new file mode 100644
index 0000000..20edb9f
--- /dev/null
+++ b/3 Resources/NFS.md
@@ -0,0 +1,32 @@
+---
+tags:
+  - linux
+  - nfs
+references:
+  - https://linux.die.net/man/5/exports
+  - https://wiki.gentoo.org/wiki/Nfs-utils
+  - https://docs.freebsd.org/en/books/handbook/network-servers/#network-nfs
+---
+# Server
+daemons: 
+- nfsd : handles reqs from nfs clients
+- mountd : handles reqs from nfsd
+- rpcbind : allows nfs clients to discover which port the NFS server is using
+# Exports
+`/etc/exports` contains table of FS' that are exported over NFS. Newline-seperated list of exports that are in turn whitespace seperated with clients allowed to mount there. A client can be followed by parenthesised comma-seperated list of export opts.
+Default opts can be specified at the end behind a dash.
+
+**Client specs**
+- Single host (name or ip)
+- Netgroups
+- Wildcards (`?` or `*` and `[]` char classes)
+- IP networks (`ipaddr/netmask` )
+
+**Some useful options**
+- rw
+- ro
+
+**Example**
+```
+/nfs 192.168.50.0/24(rw,sync,insecure,no_subtree_check)
+```
\ No newline at end of file
diff --git a/3 Resources/Nix/Adding things to the nix store.md b/3 Resources/Nix/Adding things to the nix store.md
new file mode 100644
index 0000000..98b2c17
--- /dev/null
+++ b/3 Resources/Nix/Adding things to the nix store.md
@@ -0,0 +1,12 @@
+---
+tags:
+  - nix
+---
+It's possible to use `nix-prefetch-url`:
+```
+nixos main
+❯ nix-prefetch-url --name displaylink-610.zip https://www.synaptics.com/sites/default/files/exe_files/2024-10/DisplayLink%20USB%20Graphics%20Software%20for%20Ubuntu6.1-EXE.zip
+path is '/nix/store/a10lxg1y9hc5ida4npg2mrmymc8932hl-displaylink-610.zip'
+1b3w7gxz54lp0hglsfwm5ln93nrpppjqg5sfszrxpw4qgynib624
+
+```
\ No newline at end of file
diff --git a/3 Resources/Nix/Cleaning the Nix store.md b/3 Resources/Nix/Cleaning the Nix store.md
new file mode 100644
index 0000000..4ec07c0
--- /dev/null
+++ b/3 Resources/Nix/Cleaning the Nix store.md
@@ -0,0 +1,11 @@
+---
+tags:
+  - nix
+references:
+  - https://www.reddit.com/r/NixOS/comments/10107km/how_to_delete_old_generations_on_nixos/
+  - https://nixos.org/manual/nixos/unstable/#sec-nix-gc
+---
+```
+sudo nix-collect-garbage -d
+sudo nixos-rebuild boot 
+```
\ No newline at end of file
diff --git a/3 Resources/Nix/Flake.md b/3 Resources/Nix/Flake.md
index 754556f..d191989 100644
--- a/3 Resources/Nix/Flake.md
+++ b/3 Resources/Nix/Flake.md
@@ -18,5 +18,67 @@ In flakes dependencies have to be specified explicitly and MUST be locked to spe
 Output of a Flake is an arbitrary [[Zettelkast/Index/Nix]] value such as a package, [[NixOS]] module or library function.
 Commands `nix build` and `nix shell` will build the output `packages.<system>.default` unless we specify another output, for example: `nix shell .#checks.aarch64-linux.build`.
 
+
+**Inputs**
+```
+{
+  inputs = {
+    # GitHub repository as the data source, specifying the master branch.
+    # This is the most common input format.
+    nixpkgs.url = "github:Mic92/nixpkgs/master";
+    # Git URL, applicable to any Git repository using the https/ssh protocol.
+    git-example.url = "git+https://git.somehost.tld/user/path?ref=branch";
+    # Git URL by tag, applicable to any Git repository using the https/ssh protocol.
+    git-example-tag.url = "git+https://git.somehost.tld/user/path?tag=x.y.x";
+    # Github URL by pull request.
+    git-pr.url = "github:NixOS/nixpkgs?ref=pull/349351/head";
+    # Git URL with submodules, applicable to any Git repository using the https/ssh protocol. 
+    git-example-submodule.url = "git+https://git.somehost.tld/user/path?submodules=1";
+    # Archive File URL, needed in case your input use LFS.
+    # Regular git input doesn't support LFS yet.
+    git-example-lfs.url = "https://codeberg.org/solver-orgz/treedome/archive/master.tar.gz";
+    # Similar to fetching a Git repository, but using the ssh protocol
+    # with key authentication. Also uses the shallow=1 parameter
+    # to avoid copying the .git directory.
+    ssh-git-example.url = "git+ssh://git@github.com/ryan4yin/nix-secrets.git?shallow=1";
+    # It's also possible to directly depend on a local Git repository.
+    git-directory-example.url = "git+file:/path/to/repo?shallow=1";
+    # Using the `dir` parameter to specify a subdirectory.
+    nixpkgs.url = "github:foo/bar?dir=shu";
+    # Local folder (if using an absolute path, the 'path:' prefix can be omitted).
+    directory-example.url = "path:/path/to/repo";
+
+    # If the data source is not a flake, set flake=false.
+    # `flake=false` is usually used to include additional source code,
+    #   configuration files, etc.
+    # In Nix code, you can directly reference files within
+    #   it using "${inputs.bar}/xxx/xxx" notation.
+    # For example, import "${inputs.bar}/xxx/xxx.nix" to import a specific nix file,
+    # or use "${inputs.bar}/xx/xx" as a path parameter for certain options.
+    bar = {
+      url = "github:foo/bar/branch";
+      flake = false;
+    };
+
+    sops-nix = {
+      url = "github:Mic92/sops-nix";
+      # `follows` is the inheritance syntax within inputs.
+      # Here, it ensures that sops-nix's `inputs.nixpkgs` aligns with
+      # the current flake's inputs.nixpkgs,
+      # avoiding inconsistencies in the dependency's nixpkgs version.
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
+    # Lock the flake to a specific commit.
+    nix-doom-emacs = {
+      url = "github:vlaci/nix-doom-emacs?rev=238b18d7b2c8239f676358634bfb32693d3706f3";
+      flake = false;
+    };
+  };
+
+  outputs = { self, ... }@inputs: { ... };
+}
+```
+
 ---
 [Flakes Wiki](https://nixos.wiki/wiki/Flakes)
\ No newline at end of file
diff --git a/3 Resources/Nix/Functional programming vs imperative.md b/3 Resources/Nix/Functional programming vs imperative.md
new file mode 100644
index 0000000..8c2619a
--- /dev/null
+++ b/3 Resources/Nix/Functional programming vs imperative.md
@@ -0,0 +1,26 @@
+---
+tags:
+  - programming
+  - nix
+---
+While working on a NixOS module I made a realisation on the difference between functional and imperative programming.
+I was trying to configure `systemd.tmpfiles.rules` to create directories for git repositories. After looking a bit how to iterate; i tried the following:
+```nix
+let
+  paths = ["abs_paths" ...]
+in
+{
+  map(p: systemd.tmpfiles.rules = ["d {$p} ..."];);
+}
+```
+This is very much originating from the imperative mindset; we loop over a list and then do stuff like setting variables and calling other functions. However in functional programming we do not! This is the correct version in functional programming:
+```nix
+let
+  paths = [ "abs_paths" ... ];
+in
+{
+  systemd.tmpfiles.rules = map(p: "d ${p} ..") paths;
+}
+```
+
+Functions are pure, we can't assign stuff inside of their bodies because that would make them impure. Instead we can just return a value; in this case an array and *then* assign it.
\ No newline at end of file
diff --git a/3 Resources/Nix/Generating Nix expressions.md b/3 Resources/Nix/Generating Nix expressions.md
new file mode 100644
index 0000000..347a7af
--- /dev/null
+++ b/3 Resources/Nix/Generating Nix expressions.md
@@ -0,0 +1,7 @@
+---
+tags:
+  - nix
+---
+From this repo it looks like we can convert JSON into Nix using `nix-instantiate --expr --eval builtins.fromJSON <jsonfile> `
+
+https://github.com/Janik-Haag/nm2nix/blob/main/nm2nix.py
\ No newline at end of file
diff --git a/3 Resources/Nix/Home-manager systemd.md b/3 Resources/Nix/Home-manager systemd.md
new file mode 100644
index 0000000..d4a1460
--- /dev/null
+++ b/3 Resources/Nix/Home-manager systemd.md
@@ -0,0 +1,35 @@
+---
+tags:
+  - nix
+  - home-manager
+  - systemd
+---
+Config options start with `systemd.user`
+
+Home-manager manages the enabling and such based on the dependencies of the unit.
+So we can something like
+```
+Install = {
+  WantedBy = [ "default.target" ];
+};
+```
+
+And it will enable it.
+
+Another example
+```nix
+systemd.user.services.astal = {
+  Unit = {
+    Description = "Runs the astal bar instance";
+    After = [ "graphical-session-pre.target" ];
+  };
+  Service = {
+    Type = "exec";
+    ExecStart = "some-bin";
+  };
+
+  Install = {
+    WantedBy = [ "graphical-session.target" ];
+  };
+};
+```
\ No newline at end of file
diff --git a/3 Resources/Nix/Hostname changes.md b/3 Resources/Nix/Hostname changes.md
new file mode 100644
index 0000000..0aaa324
--- /dev/null
+++ b/3 Resources/Nix/Hostname changes.md
@@ -0,0 +1,6 @@
+---
+tags:
+  - nixos
+  - nixos-anywhere
+---
+When using nixos-anywhere and passing it a hostname; it changes during kexec to nixos-anywhere. But the script will continue attempting to connect to whatever we gave it. Therefore we should pass it an IP address instead.
\ No newline at end of file
diff --git a/3 Resources/Nix/Interpolation.md b/3 Resources/Nix/Interpolation.md
new file mode 100644
index 0000000..bbdb457
--- /dev/null
+++ b/3 Resources/Nix/Interpolation.md
@@ -0,0 +1,7 @@
+---
+tags:
+  - nix
+references:
+  - https://nix.dev/manual/nix/2.24/language/syntax#string-literal
+---
+In a normal string we can use backslash to escape. In indented strings we should use double backticks.
\ No newline at end of file
diff --git a/3 Resources/Nix/Nix Manual References.md b/3 Resources/Nix/Nix Manual References.md
new file mode 100644
index 0000000..486a2fe
--- /dev/null
+++ b/3 Resources/Nix/Nix Manual References.md
@@ -0,0 +1,7 @@
+---
+tags:
+  - nix
+references:
+  - https://nix.dev/manual/nix/2.24/language/builtins.html
+  - https://nixos.org/manual/nixpkgs/stable
+---
diff --git a/3 Resources/Nix/Nix collect garbage.md b/3 Resources/Nix/Nix collect garbage.md
new file mode 100644
index 0000000..65e6aad
--- /dev/null
+++ b/3 Resources/Nix/Nix collect garbage.md
@@ -0,0 +1,10 @@
+---
+tags:
+  - nix
+references:
+  - https://www.reddit.com/r/NixOS/comments/10107km/how_to_delete_old_generations_on_nixos/
+---
+```
+sudo nix-collect-garbage -d
+sudo nixos-rebuild boot 
+```
\ No newline at end of file
diff --git a/3 Resources/Nix/NixOS Modules.md b/3 Resources/Nix/NixOS Modules.md
new file mode 100644
index 0000000..1ab4c25
--- /dev/null
+++ b/3 Resources/Nix/NixOS Modules.md
@@ -0,0 +1,56 @@
+---
+tags:
+  - nix
+  - nixos
+references:
+  - https://nixos.org/manual/nixos/unstable/#sec-writing-modules
+  - https://nixos.org/manual/nixpkgs/stable/#module-system-lib-evalModules
+  - https://nix.dev/tutorials/module-system/
+  - llk
+---
+Extra care must be taken when writing systemd services using Exec* due to interpolation and such. `utils.escapeSystemdExecArg` and `utils.escapeSystemdExecArg` exist.
+
+```nix
+{
+  options = {
+    name = mkOption {
+      type = type specification;
+      default = default value;
+      example = example value;
+      description = "Description for use in the NixOS manual.";
+    };
+  };
+}
+```
+
+**A list of submodules**
+```nix
+{
+  options.mod = mkOption {
+    description = "submodule example";
+    type = with types; listOf (submodule {
+      options = {
+        foo = mkOption {
+          type = int;
+        };
+        bar = mkOption {
+          type = str;
+        };
+      };
+    });
+  };
+}
+```
+
+
+**Testing**
+```nix eval.nix
+let
+	pkgs = import <nixpkgs> {};
+	res = pkgs.lib.evalModules {
+		modules = [./git-repos.nix];
+	};
+in
+res.config
+```
+`nix-instantiate --eval eval.nix`
\ No newline at end of file
diff --git a/3 Resources/Nix/Remote nixos rebuild lacking valid signature.md b/3 Resources/Nix/Remote nixos rebuild lacking valid signature.md
new file mode 100644
index 0000000..82e03b2
--- /dev/null
+++ b/3 Resources/Nix/Remote nixos rebuild lacking valid signature.md
@@ -0,0 +1,13 @@
+---
+tags:
+  - nix
+  - nixos
+references:
+  - https://nixos.wiki/wiki/Nixos-rebuild
+---
+When rebuilding on a remote it might spew an error containing: "is lacking a valid signature". To remedy this we need to add our non-root user as a trusted user;
+```
+nix.extraOptions = ''
+  trusted-users jras
+'';
+```
\ No newline at end of file
diff --git a/3 Resources/Nix/Shell.nix.md b/3 Resources/Nix/Shell.md
index 13715c2..08e7c53 100644
--- a/3 Resources/Nix/Shell.nix.md
+++ b/3 Resources/Nix/Shell.md
@@ -1,6 +1,35 @@
-#nix #shell
-
 ---
+tags:
+  - nix
+  - shell
+---
+Basic invocation: `nix-shell -p [ pkgs ... ]`
+
+# Shebang
+```
+#! /usr/bin/env nix-shell
+#! nix-shell -i bash -p bash
+
+do stuff
+```
+
+Different interpreters can be set with the `-i` option such as python
+```
+#! /usr/bin/env nix-shell
+#! nix-shell -i python3 -p python3
+
+print("hello world")
+```
+
+The `-I` option can be used to pin nixpkgs
+```
+#! /usr/bin/env nix-shell
+#! nix-shell -i bash
+#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/aed4b19d312525ae7ca9bceb4e1efe3357d0e2eb.tar.gz
+
+echo hello world
+```
+# Shell.nix
 Can be used to set up per dir environments, e.g using direnv to automatically activate them.
 ## Python
 https://nixos.org/manual/nixpkgs/stable/#python
@@ -38,5 +67,5 @@ let
 in python311.withPackages (ps: with ps; [ numpy my_toolz ]) ).env
 ```
 
-The [[Import]] is required here because imports a nix expression from another source, in this case nixpkgs.
+					The [[Import]] is required here because imports a nix expression from another source, in this case nixpkgs.
 It is not required at line two, because python310Packages itself is already in the local scope.
\ No newline at end of file
diff --git a/3 Resources/Programming/Integer types Rust.png b/3 Resources/Programming/Integer types Rust.png
new file mode 100644
index 0000000..358eb85
--- /dev/null
+++ b/3 Resources/Programming/Integer types Rust.png
diff --git a/3 Resources/Programming/Rust.md b/3 Resources/Programming/Rust.md
new file mode 100644
index 0000000..8724ca3
--- /dev/null
+++ b/3 Resources/Programming/Rust.md
@@ -0,0 +1,27 @@
+https://rust-book.cs.brown.edu
+
+> Finished chapter 2. Onto chapter 3!
+
+If the name ends with ! it's a macro.
+
+By default, Rust has a set of items defined in the standard library that it brings into the scope of every program. This set is called the _prelude_, and you can see everything in it [in the standard library documentation](https://doc.rust-lang.org/std/prelude/index.html).
+
+"he `stdin` function returns an instance of [`std::io::Stdin`](https://doc.rust-lang.org/std/io/struct.Stdin.html), which is a type that represents a handle to the standard input for your terminal."
+How does this work? How does it know which terminal is ours? I guess it might be connected by linux when running the process as `/proc/<pid>/stdin`.
+
+`&` is a reference. References are also immutable by default, thus `&mut guess` will allow us to update the reference to the variable guess.
+
+Enum members are called variants.
+
+`cargo doc --open` command will build documentation provided by all your dependencies locally and open it in your browser.
+
+`match`  expression -> arms -> pattern +  code path. Match expressions stop evaluating if a match is made; therefore we should strive to order them based on their likeliness to be hit.
+
+`shadowed` = when a variable name is used multiple times; e.g
+```
+let x = 1
+let x = 2 <- shadowed
+```
+Shadowing is different from making a variable `mutable` because it is fully reassigned (thus its type can also be changed), but the value is then still immutable (giving compiler errors when we try to reassign).
+
+![[Integer types Rust.png]]
\ No newline at end of file
diff --git a/3 Resources/Python/Make dataclass dict-able.md b/3 Resources/Python/Make dataclass dict-able.md
index d8ee02b..7cb391b 100644
--- a/3 Resources/Python/Make dataclass dict-able.md
+++ b/3 Resources/Python/Make dataclass dict-able.md
@@ -12,4 +12,9 @@ We can use `vars` to make that easy:
 def __iter__(self):
   for k, v in vars(self):
     yield k, v
+```
+
+> This only works when all vars are primtiives, a list of objects for example needs nested iteration. Example:
+```
+yield "volumes", [iter(vol) for vol in self.volumes]
 ```
\ No newline at end of file
diff --git a/3 Resources/Python/Python dunder.md b/3 Resources/Python/Python dunder.md
new file mode 100644
index 0000000..ca24307
--- /dev/null
+++ b/3 Resources/Python/Python dunder.md
@@ -0,0 +1,6 @@
+---
+tags:
+  - python
+---
+Everything in python is an object, even strings, functions etc.
+all operations are defined as dunder methods; eg  "bla" + "bla" == str.\_\_add\_\_
diff --git a/3 Resources/SQLAlchemy/2.0 query style operator reference.md b/3 Resources/SQLAlchemy/2.0 query style operator reference.md
new file mode 100644
index 0000000..5161d1c
--- /dev/null
+++ b/3 Resources/SQLAlchemy/2.0 query style operator reference.md
@@ -0,0 +1,7 @@
+---
+tags:
+  - sqlalchemy
+references:
+  - https://docs.sqlalchemy.org/en/20/core/operators.html
+---
+The referenced link is very useful when working with the 2.0-style query. For example, i was figuring out how to add a IN clause to a query and it's documented in there (`in_`).
\ No newline at end of file
diff --git a/3 Resources/System feedback.md b/3 Resources/System feedback.md
new file mode 100644
index 0000000..97b97a1
--- /dev/null
+++ b/3 Resources/System feedback.md
@@ -0,0 +1,9 @@
+---
+tags:
+  - system-design
+  - software-design
+  - design
+---
+I read an article somewhere about control plane feedback: any action we take should give (direct) feedback.
+
+This idea can be extended to a control panel implementation, e.g an openstack control panel. Where any action you do provides you with instant feedback. Think of creating a server; but it fails somewhere down the line due to an IP being allocated already. We want to know that so we can try again with another IP.
\ No newline at end of file
diff --git a/3 Resources/Systemd/Systemd restart signal.md b/3 Resources/Systemd/Systemd restart signal.md
new file mode 100644
index 0000000..3497069
--- /dev/null
+++ b/3 Resources/Systemd/Systemd restart signal.md
@@ -0,0 +1,25 @@
+---
+tags:
+  - systemd
+  - restart
+references:
+  - https://www.reddit.com/r/linuxquestions/comments/10eu3i0/does_systemctl_restart_send_sigterm_signal/?rdt=64556
+---
+By default, `restart` does exactly the same thing as `stop` followed by `start`.
+
+`stop` will:
+
+- execute `ExecStop=` commands, if any;
+    
+- send the signal defined by `KillSignal=` (default: `SIGTERM`), to any remaining processes identified by the `KillMode=`;
+    
+- send `SIGCONT` to those same processes;
+    
+- if `SendSIGHUP=` is true (default: false), send `SIGHUP` to those same processes;
+    
+- if `SendSIGKILL=` is true (default: true), and any processes remain after `TimeoutStopSec=`, send the `FinalKillSignal=` (default: `SIGKILL`) to those remaining processes;
+    
+- execute `ExecStopPost=` commands, if any.
+    
+
+`restart` changes this by using `RestartKillSignal=` instead of `KillSignal=`, but if `RestartKillSignal=` is not set it just inherits its value from `KillSignal=`. And, of course, `restart` then performs all the regular `start` actions after everything else. `restart` also differs from `stop` by not flushing the file descriptor store associated with the service.
\ No newline at end of file
diff --git a/3 Resources/Systemd/Unit types.md b/3 Resources/Systemd/Unit types.md
index 27ee387..51bb40f 100644
--- a/3 Resources/Systemd/Unit types.md
+++ b/3 Resources/Systemd/Unit types.md
@@ -5,10 +5,13 @@ tags:
 ---
 The `Type` directive is specified within the `Service` section. There are 6 different types;
 - **Simple**: The default if `Type` nor `Busname` are specified.
+- **Exec** : similar to simple but waits a bit more for the service to be started successfully
 - **Forking**: Used when the parent process exits immediately due to it forking. Systemd will know it's still running even though it exited.
 - **Oneshot**: When the process is short-lived and doesn't need to keep running. Systemd will wait on the process before starting other units.
 - **Dbus**: The process will be registered on the D-Bus bus.
 - **Notify**: Systemd will expect a notification from the process to signal it has started up blocking the execution of other units until the signal is received.
 - **Idle**: Service will not run ufntil all jobs are dispatched. #clarify
 
-https://www.digitalocean.com/community/tutorials/understanding-systemd-units-and-unit-files#unit-specific-section-directives
\ No newline at end of file
+https://www.digitalocean.com/community/tutorials/understanding-systemd-units-and-unit-files#unit-specific-section-directives
+
+**Exec** is recommended by `man systemd.service` for long-running services.
\ No newline at end of file
diff --git a/3 Resources/Tailscale.md b/3 Resources/Tailscale.md
new file mode 100644
index 0000000..6cf82c4
--- /dev/null
+++ b/3 Resources/Tailscale.md
@@ -0,0 +1,16 @@
+---
+tags:
+  - tailscale
+  - vpn
+references:
+  - https://tailscale.com/blog/tailscale-key-management
+---
+# About keys
+Two types of keys: machine keys and node keys.
+
+The machine key is tied to a specific machine and is used during pre-authorization (started when it first attempts to join a network).
+
+When successfully added to a network a node key is generated on the client. The public component is tied to the machine key on the control server.
+The node key is also tied to an identity; via the URL that's sent back to the client and then used to login.
+
+The public node key is then distributed to other nodes it's allowed to communicate with.
\ No newline at end of file
diff --git a/3 Resources/Techniques/Long polling.md b/3 Resources/Techniques/Long polling.md
new file mode 100644
index 0000000..7cbabd0
--- /dev/null
+++ b/3 Resources/Techniques/Long polling.md
@@ -0,0 +1 @@
+Poll req client -> server keeps open conn, puts req in queue to be processed later, processor picks up from Q and responds to client.
\ No newline at end of file
diff --git a/3 Resources/ansible/Waiting for stuff.md b/3 Resources/ansible/Waiting for stuff.md
new file mode 100644
index 0000000..e00bb19
--- /dev/null
+++ b/3 Resources/ansible/Waiting for stuff.md
@@ -0,0 +1,12 @@
+---
+tags:
+  - ansible
+references:
+  - https://docs.ansible.com/ansible/latest/collections/ansible/builtin/wait_for_module.html
+---
+There's a module to wait for all sorts of stuff, e.g a file being created or removed:
+```yaml
+  ansible.builtin.wait_for:
+    path: /opt/puppetlabs/puppet/cache/state/agent_catalog_run.lock
+    state: absent
+```
diff --git a/3 Resources/jq/about.md b/3 Resources/jq/about.md
new file mode 100644
index 0000000..09da541
--- /dev/null
+++ b/3 Resources/jq/about.md
@@ -0,0 +1,11 @@
+---
+tags:
+  - jq
+  - json
+---
+`jq` is a filter program. Everything , including literals, are `filters` in jq.
+filter have input and output.
+ops that combine filters like addition or division feed same input to both filters before doing the operation e.g `[1 2 3] | add / length` < array is passd to both add and length and then de division is done.
+
+identity filter use quotes or brackets and quotes if name has special values such as whitespace. `."Fo o"` || `.["Fo o"]`
+
diff --git a/3 Resources/jq/arrays.md b/3 Resources/jq/arrays.md
new file mode 100644
index 0000000..83373c2
--- /dev/null
+++ b/3 Resources/jq/arrays.md
@@ -0,0 +1,10 @@
+---
+tags:
+  - jq
+---
+To access a specific index we can just access it by index nr
+```
+Command jq '.[0]'
+Input  [{"name":"JSON", "good":true}, {"name":"XML", "good":false}]|
+Output {"name":"JSON", "good":true}|
+```
\ No newline at end of file
diff --git a/3 Resources/libvirt/Using Virsh to manage bitmaps.md b/3 Resources/libvirt/Using Virsh to manage bitmaps.md
new file mode 100644
index 0000000..5cb41f3
--- /dev/null
+++ b/3 Resources/libvirt/Using Virsh to manage bitmaps.md
@@ -0,0 +1,23 @@
+---
+tags:
+  - libvirt
+  - qemu
+references:
+  - https://qemu-project.gitlab.io/qemu/interop/bitmaps.html
+---
+To query info about block devices, including bitmaps we can use a QMP command:
+```
+sudo virsh qemu-monitor-command --pretty instance-00026133 '{"execute": "query-block", "arguments": {}}'
+```
+
+There are six primary bitmap-management API commands:
+- `block-dirty-bitmap-add`
+- `block-dirty-bitmap-remove`
+- `block-dirty-bitmap-clear`
+- `block-dirty-bitmap-disable`
+- `block-dirty-bitmap-enable`
+- `block-dirty-bitmap-merge`
+And one related query command:
+- `query-block`
+
+The `node` argument to bitmap cmds can be found as `node-name` in `query-block` results.
\ No newline at end of file
diff --git a/3 Resources/sysapi/create_cluster.json b/3 Resources/sysapi/create_cluster.json
new file mode 100644
index 0000000..e40067e
--- /dev/null
+++ b/3 Resources/sysapi/create_cluster.json
@@ -0,0 +1,9 @@
+{
+  "data": {
+    "attributes": {
+      "legacy_domain": false,
+      "region_name": "EU"
+    },
+    "type": "clusters"
+  }
+}
diff --git a/3 Resources/sysapi/create_cluster.sh b/3 Resources/sysapi/create_cluster.sh
new file mode 100755
index 0000000..d07b48f
--- /dev/null
+++ b/3 Resources/sysapi/create_cluster.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env nix-shell
+#! nix-shell -i bash -p curl
+
+curl -d @create_cluster.json -n https://systemsapi.one.com/v3/brands/test.groupone.dev/clusters
+
diff --git a/3 Resources/sysapi/enable_vps.json b/3 Resources/sysapi/enable_vps.json
new file mode 100644
index 0000000..1c5567a
--- /dev/null
+++ b/3 Resources/sysapi/enable_vps.json
@@ -0,0 +1,8 @@
+{
+  "data": {
+    "attributes": {
+      "provisioned": true
+    },
+    "type": "services"
+  }
+}
diff --git a/3 Resources/sysapi/patch_vps.sh b/3 Resources/sysapi/patch_vps.sh
new file mode 100755
index 0000000..63b181b
--- /dev/null
+++ b/3 Resources/sysapi/patch_vps.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env nix-shell
+#! nix-shell -i bash -p curl
+
+curl -X PATCH -d @enable_vps.json -n https://systemsapi.one.com/v3/brands/test.groupone.dev/clusters/c0efmoghy/services/vps
+