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

13 files changed, 143 insertions, 1 deletions

diff --git a/3 Resources/Linux/BatchMode.md b/3 Resources/Linux/BatchMode.md
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--- /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.
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diff --git a/3 Resources/Linux/Create  bootable USB.md b/3 Resources/Linux/Create  bootable USB.md
new file mode 100644
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+++ 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
+```
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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
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+++ 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>`
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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.
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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
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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
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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
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+++ 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!
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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
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+++ 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
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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,.
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