Common Shell Commands

Shell

Shortcut

Key Description
<C-b> Move back a char
<C-f> Move forward a char
<M-b> Move back a word
<M-f> Move forward a word
<C-s> Pause STDOUT
<C-q> Resume STDOUT
<C-r> Enter history search mode
<C-g> Leave history search mode (Or break out a newline)
<C-m> Same as <CR> (Enter key)
<M-h> Open manual for current command
  • type Show command type (built-in or outer);
  • whereis Show program path and its manual;
  • whatis Show a program's manual.
  • help xxx Fast help for shell built-in commands.
  • history Show shell history, which can be used along with fc.

Redirects:

  • Redirecting Output (Write, override) >
  • Appending Redirected Output >>
  • Here Strings <<<

  • Here Documents

    $ cat <<[-]EOF
111
222
333
EOF

    The optional - trims the <tab>.

  • Process Substitution
    $ cat <(echo 233)

Shell Variables

  • $#: Number of arguments
  • $$ (same as ${$}): Current shell's PID.
  • declare -i defines integer variable
    $ x=5; y=3
$ declare -i z=$x+$y
$ z=z+3 # Integer variable can do arithmetic directly
$ k=$(($x+$y)) # Do arithmetic but the type of 'k' still remains string
  • Shell for loop
    #!/bin/sh
for ((i=0; i<=10; i=i+1)); do
  printf " $i"
done
printf "\n"
for i in {0..10}; do
  printf " $i"
done
printf "\n"
for i in {0..10..2}; do # Step = 2
  printf " $i"
done
printf "\n"
# Results:
#  0 1 2 3 4 5 6 7 8 9 10
#  0 1 2 3 4 5 6 7 8 9 10
#  0 2 4 6 8 10
  • Shell's Functions
    #!/bin/sh
function sum() {
   echo $# # 
   echo $* # Parameters in string type
   echo $0 # The 0st parameter, which is the name of executed file itself
   echo $1 # The first parameter
   echo $@ # Parameters in an array type
}
sum 1 2 7 'a'
# Results:
# 4
# 1 2 7 a
# ./sum.sh
# 1
# 1 2 7 a

  • How do shell arguments be processed with stdin, stdout, stderr:

    #include<stdio.h>
int main(int argc, char *argv[]) {
  int i = 0;
  char c;

  for (; i < argc; ++i) fprintf(stdout, "%d: %s\n", i, argv[i]);
  fflush(stdout);

  c = fgetc(stdin);
  while (c != EOF) { // Convert to UPPERCASE
    if (c >= 'a' && c <= 'z') c += 'A' - 'a';
    fputc(c, stdout);
    c = fgetc(stdin);
  }
  fflush(stdout);

  fprintf(stderr, "I am stderr\n");
  fflush(stderr);
}

    clang test.c -o test
./test 1 2 3 a b c <<EOF
hello world
aaaaaaa
EOF

Glob Extension

Exclusive Delete

  • Bash
    $ shopt -s extglob
$ rm -r !(file1|file2|dir)
  • Zsh
     $ setopt extendedglob
 $ rm -r ^(file1|file2|dir)

Trap

Reset signal TERM's action to the default: trap - TERM

Signal Number Signal Name Default Action
0 EXIT Nothing
2 INT Terminate (Interrupt, weakest, Ctrl+C)
15 TERM Terminate (Exit cleanly, normal)
1 HUP Terminate (Hangup, normal, sent from SSH disconnect)
3 QUIT Terminate (Harshest but still handle ignorable, core dump)
9 KILL Terminate (Unconditionally)

IF Statement in Bash

  • Integer Operator
    -eq    equal
-ne    not equal
-gt    greater
-ge    geeater or equal
-lt    lesser
-le    lesser or equal
  • File Operator
    -e          File or directory exist
-r          Readable
-w          Writable
-x          Executable
-f          Whether a normal file
-d "dir"    Whether a directory exists
! -d "dir"  Whether a directioy not exists
-c          Whether a char file
-b          Whether a block file
-s          Ture if file size is not zero
-t          Whether a tty file
  • String Operator
    # POSIX sh
str1 = str2
str1 > str2    Compare by alphabetical order
str1 < str2
-z str         True if the string length is zero
-n str         True if the string length is non-zero
# Bash specific (Can use pattern matching '[[' ']]')
str1 == str2
str1 != str2
str1 =~ regex  Extended regular expression
  • Logical Operator
    -a        And
-o        Or
!         Not
[] && []  And (For pattern matching use '[[' ']]')
[] || []  Or

Bash Extended Globbing

Glob Regular Expression Equivalent
* .*
? .
[a-z] SAME
?(pattern) (regex)?
*(pattern) (regex)*
+(pattern) (regex)+
@(pattern) (regex){1}
!(pattern) ^((?!regex).)*$

Variable Parameter Expansions

Key Description
::n Cut n chars from left to right if n is positive, otherwise right to left if negative
:n Cut to end start from column n, if n is negative then right to left (use :(-n) or : -n)
:x:y Cut y chars start from column x
${food:-Cake} Defaults to Cake if $food does not exist
STR="/path/to/foo.cpp" Description
echo ${STR%/*} # /path/to Cut from right to left, single % means non-greedy
echo ${STR#*/} # path/to/foo.cpp Cut from left to right, single # means non-greedy
echo ${STR%.cpp} # /path/to/foo Two % is greedy
echo ${STR##*.} # cpp Two # is greedy
echo ${STR/foo/bar} # /path/to/bar.cpp String substitution, single / means non-greedy
echo ${STR//o/b} # /path/tb/fbb.cpp Two / is greedy

set

set -eufo pipefail

  • -e let bash exit immediately if any command has non-zero exit status.
  • -u let bash exit immediately if there are any reference to variable haven't defined yet.
  • -f disables pathname expansion (globbing).
  • -o pipefail prevents error in pipeline from being masked. Any command fails in pipeline will keep its return code for whole pipeline.

Reset User Fail Lock

$ faillock --user <username> --reset

Binary File Editing Modification

Generate a hex dump:

$ xxd TIAS2781RCA4.bin > TIAS2781RCA4.bin.txt

Revert plaintext hex dump back into binary:

$ cat TIAS2781RCA4.bin.txt | xxd -r > TIAS2781RCA4_mod.bin

PDF Editing

PDF Extracting:

$ pdfimages -all in.pdf out_dir/

PDF Regenerate:

$ img2pdf --output out.pdf \
--creator 'Canon SC1011' \
--producer 'IJ Scan Utility' \
--creationdate 'Wed Mar 20 16:33:38 2024 CST' \
-D \
--engine internal \
-s 600dpi \
[1-5].jpg
$ pdfinfo out.pdf

Gamescope

Launch a game with FSR1, VRR, MangoHud in Steam:

$ gamescope -w 1728 -h 1080 -W 2944 -H 1840 --adaptive-sync -F fsr --fsr-sharpness 10 -- env LD_PRELOAD='/usr/lib/mangohud/libMangoApp.so /usr/lib/mangohud/libMangoHud.so /usr/lib/mangohud/libMangoHud_dlsym.so /usr/lib/mangohud/libMangoHud_opengl.so' sh ./cream.sh %command%

Use the Manager permission to query:

ldapsearch -x \
-H 'ldaps://proteus-nuc.tailba6c3f.ts.net:636' \
-D'cn=Manager,dc=tailba6c3f,dc=ts,dc=net' \
-W \
-b'ou=People,dc=tailba6c3f,dc=ts,dc=net' \
'(objectClass=*)' | less

Libvirt

Run --print-xml | less to dump .xml for debugging.

  • Install an Arm Cortex-A53 machine
    $ virt-install --connect qemu:///system \
--memory 2048 --memorybacking hugepages.page0.size=2048 \
--arch=aarch64 --cpu cortex-a53 --machine virt \
--vcpus vcpu=4,vcpu.placement=static --iothreads 1 \
--cputune vcpupin0.vcpu=0,vcpupin0.cpuset=2,vcpupin1.vcpu=1,vcpupin1.cpuset=10,vcpupin2.vcpu=2,vcpupin2.cpuset=3,vcpupin3.vcpu=3,vcpupin3.cpuset=11,emulatorpin.cpuset='1,9',iothreadpin0.iothread=1,iothreadpin0.cpuset='1,9' \
--cpu topology.sockets=1,topology.dies=1,topology.cores=4,topology.threads=1,numa.cell0.memory=2048,numa.cell0.unit=MiB,numa.cell0.memAccess=shared \
--osinfo archlinux \
--disk size=10,format=qcow2,driver.cache=none,driver.io=native,driver.discard=unmap,driver.iothread=1,driver.queues=4,driver.iommu=on,target.bus=virtio \
--boot firmware=efi,loader=/usr/share/edk2/aarch64/QEMU_CODE.fd,loader.readonly=yes,loader.type=pflash,nvram.template=/usr/share/edk2/aarch64/QEMU_VARS.fd,boot0.dev=network,boot1.dev=hd \
--features gic.version=3,kvm.hidden.state=off,pmu.state=on \
--clock offset=localtime,timer0.name=rtc,timer0.tickpolicy=catchup,timer0.track=guest,timer1.name=pit,timer1.tickpolicy=delay \
--network direct,trustGuestRxFilters=yes,source=macvtap0,source.mode=vepa,model=virtio,driver.iommu=on \
--controller virtio-serial,driver.iommu=on \
--video virtio,model.vram=16384,model.heads=1 \
--watchdog i6300esb \
--rng /dev/random,model=virtio,driver.iommu=on \
--tpm emulator,backend.version=2.0 \
--memballoon virtio,driver.iommu=on \
--iommu virtio \
--panic pvpanic \
--import
  • Install a RISC-V machine
    $ virt-install --connect qemu:///system \
--memory 2048 --memorybacking hugepages.page0.size=2048 \
--arch riscv64 --machine virt \
--vcpus vcpu=4,vcpu.placement=static --iothreads 1 \
--cputune vcpupin0.vcpu=0,vcpupin0.cpuset=2,vcpupin1.vcpu=1,vcpupin1.cpuset=10,vcpupin2.vcpu=2,vcpupin2.cpuset=3,vcpupin3.vcpu=3,vcpupin3.cpuset=11,emulatorpin.cpuset='1,9',iothreadpin0.iothread=1,iothreadpin0.cpuset='1,9' \
--cpu topology.sockets=1,topology.dies=1,topology.cores=4,topology.threads=1,numa.cell0.memory=2048,numa.cell0.unit=MiB,numa.cell0.memAccess=shared \
--osinfo archlinux \
--disk size=10,format=qcow2,driver.cache=none,driver.io=native,driver.discard=unmap,driver.iothread=1,driver.queues=4,driver.iommu=on,target.bus=virtio \
--boot loader=/usr/share/qemu/opensbi-riscv64-generic-fw_dynamic.bin,boot0.dev=network,boot1.dev=hd \
--features kvm.hidden.state=off \
--clock offset=localtime,timer0.name=rtc,timer0.tickpolicy=catchup,timer0.track=guest,timer1.name=pit,timer1.tickpolicy=delay \
--network direct,trustGuestRxFilters=yes,source=macvtap0,source.mode=vepa,model=virtio,driver.iommu=on \
--controller virtio-serial,driver.iommu=on \
--video virtio,model.vram=16384,model.heads=1 \
--watchdog i6300esb \
--rng /dev/random,model=virtio,driver.iommu=on \
--tpm emulator,backend.version=2.0 \
--memballoon virtio,driver.iommu=on \
--import

OpenSSL Self signing

Generate CA certificate & private key:

$ openssl req -noenc \
-newkey EC -pkeyopt ec_paramgen_curve:P-384 -keyout ca.key.pem \
-x509 -new -sha384 -days 730 \
-subj '/C=JP/ST=Toukyouto/L=Setagayaku Kitazawa/O=Homo114514/OU=Yajuu Sa-ba-/CN=Homo home/emailAddress=sudaku233@outlook.com' \
-out ca.pem

Generate certificate signing request (CSR) & private key (optional, can reuse CA key):

$ openssl req -noenc \
-newkey EC -pkeyopt ec_paramgen_curve:P-384 -keyout server.key.pem \
-new -sha384 \
-subj '/C=JP/ST=Toukyouto/L=Setagayaku Kitazawa/O=Homo114514/OU=Yajuu Sa-ba-/CN=*.tailba6c3f.ts.net/emailAddress=sudaku233@outlook.com' \
-out server.csr.pem

Generate certificate by signing CSR with a CA certificate:

$ openssl x509 -CA ca.pem -CAkey ca.key.pem -CAcreateserial \
-days 730 -sha384 \
-extfile <(<<EOF
subjectAltName = DNS:localhost,DNS:*.tailba6c3f.ts.net
authorityKeyIdentifier = keyid,issuer
basicConstraints = CA:FALSE
keyUsage = digitalSignature, keyEncipherment
extendedKeyUsage=serverAuth
EOF
) \
-req -in server.csr.pem -out server.pem

-CAcreateserial will generate ca.srl, afterward using -CAserial ca.srl.

Show information:

$ openssl ec -text -noout -in server.key.pem
$ openssl req -text -verify -in server.csr.pem
$ openssl x509 -noout -text -in server.pem

gawk

Filter only the column 3 with value >= 90: awk '$3 >= 90 { print }', where $3 >= 90 is pattern (Optional), print is the action.

  • $0: Whole line.
  • NR: Current line number. e.g. To ignore the first line awk 'NR > 1 { print $2, $5 }'
  • BEGIN means the start of file; END means end of file. e.g. awk 'BEGIN { print "SOF" } { print } END { print "EOF" }'

  • AWK supports variables:

    e.g. Calculate sum awk 'BEGIN { sum = 0 } { sum = sum + $3 } END { avg = sum / NR; print NR, sum, avg }'

    e.g. Char count awk '{ cc = cc + length($0) + 1 } END { print NR, wc }' (Validate by wc -ml. The extra +1 is because there is \n at each end of line)

  • NF: Word count of the current line. e.g. awk '{ cc = cc + length($0) + 1; wc = wc + NF } END {print NR, cc, wc }' (To validate, run wc)
  • -F set the delimiter awk -F':'

grep

Find in files recursively:

$ grep -iRl "your-text-to-find" ./
  • -o, --only-matching Print only the matched parts;
  • -n Show line number;
  • -v Reverse match;
  • -i Case-insensitive;
  • -r Search directories recursively.

Ripgrep

$ rg --no-ignore -. -L -g \!node_modules -g \!_book -g \!yarn.lock -g \!.git "awk" ./

Arguments explanation:

  • -., --hidden Search hidden files and directories.
  • -L, --follow Follow symbolic links.
  • --no-ignore Ignore files such as .gitignore will not be respected.

Sort

Sort the third column of scores.txt: sort -n -k 3 scores.txt | less

  • -n sort defaults to ASCII code sort, use -n for numeric sort.
  • -r Reverse sort.
  • -u Remove duplicates. The difference to uniq is that uniq removes exactly same content line, while sort -u remove lines which has the same match.

Coreutils

tr

tr can convert the content to UPPERCASE/Lowercase. e.g. tr 'a-z' 'A-Z' (equivalent to tr '[:lower:]' '[:upper:]')

nohup

nohup prevents program to hang on session terminate.

e.g. nohup bash run0.sh &

Findutils

Xargs

xargs format the stdin as parameters to the command.

e.g. Calculate numbers and the symbol '-' in a pile of files find . -name '*[0-9][0-9][0-9]*.txt' | xargs egrep -o '^[0-9-]+' | wc -l.

Diff

Format explanation: Three actions: d(elete), c(hange), a(dd).

e.g. 130d129 delete line 130, then align to line 129; 249a130,131 add lines 130 and 131 to former's line 249; 271,373c163,271 replace line 163, 271 to former's line 271, 373.

dd

Backup GPT:

# dd if=/dev/sda of=gpt-partition.bin bs=512 count=34

Restore GPT

# dd if=gpt-partition.bin of=/dev/sda bs=512 count=34

DSDT (Differentiated System Description Table)

Here is an example to fix the s2idle issue on Lenovo Yoga Air 14s APU8 (aka. Yoga Slim 7 Gen 8 14APU8)

Extract & Modify DSDT

Extract the binary ACPI tables

# cat /sys/firmware/acpi/tables/DSDT > dsdt.dat

Disassemble the ACPI tables to a .dsl file

$ iasl -d dsdt.dat

Modify DSDT

$ vim dsdt.dsl

Attempt to create a hexed AML table (in C) dsdt.aml

$ iasl -tc dsdt.dsl | grep Errors

Extract & Modify SSDT (System Service Descriptor Table)

Extract SSDT

# for i in /sys/firmware/acpi/tables/SSDT*; do \
    cat $i > ${i##*/}; \
done
$ iasl -d SSDT*

Modify SSDT

$ rg "SB.PCI0.GPP8.NVME" SSDT*.dsl
$ # Found keywords in SSDT14.dsl, comment out it
$ vim SSDT14.dsl

Compile SSDT (generate .aml)

$ iasl -tc SSDT14.dsl

Create a cpio archive

$ mkdir -p kernel/firmware/acpi
$ cp dsdt.aml SSDT14.aml kernel/firmware/acpi # dsdt.aml is optional if it keep untouched
$ find ./kernel | cpio -o -H newc > SSDT14

To extract a cpio archive

$ cpio -iv -H newc < SSDT14
$ iasl -d kernel/firmware/acpi/SSDT14.aml

cpio arguments explanation:

  • -o, --create: Copy-out;
  • -H, --format=FORMAT: Use given archive FORMAT. newc is the new (SVR4) portable format;
  • -i, --extract: Copy-in;
  • -v, --verbose: Verbosely list the files processed.

Filesystem

  • A file corresponds to one inode (which stores the file properties and the pointer table of blocks, blocks store the data of the file).
  • Hard symbol links: Same file but has multiple names; Only apply to file, doesn't support directory; Can't across filesystems.
  • Soft symbol links (aka. Symlink): Different file but same name; Could apply to file or directory; Can across filesystems.
  • Why directories cannot have hard link, but it has hard link count more than 1? Because directories have pointer ./ and ../, which increase the hard link count.

Misc

  • findmnt: List all mounted filesystems.
  • List options that are set for a loaded module
    sudo systool -v -m module_name
  • Get a process's command environment variables:
    # The `-s` inspect the master process
sudo cat /proc/$(pidof -s nix-daemon)/environ | tr '\0' '\n'

Clean Build (Arch Linux)

  • Prepare
    $ RAMDISK_SIZE=$(($(free -m | awk '/Mem/ { print $7 }')/2))
$ sudo mount --mkdir -t tmpfs -o defaults,size=${RAMDISK_SIZE}M tmpfs \
/tmp/aur_chroot
$ sudo dd if=/dev/zero of=/tmp/aur_chroot/ramdisk status=progress bs=1M \
count=$RAMDISK_SIZE
$ sudo mkfs.btrfs -m single -f /tmp/aur_chroot/ramdisk
$ sudo mount --mkdir -t btrfs -o loop,sync,compress=zstd \
/tmp/aur_chroot/ramdisk /tmp/aur_chroot/overlay
$ sudo chown proteus: /tmp/aur_chroot/overlay
$ CHROOT=/tmp/aur_chroot/overlay
  • Use paru
    $ paru -S --chroot=$CHROOT <Packages>
  • Manual Way
    # mkarchroot $CHROOT/root base-devel
$ makechrootpkg -c -r $CHROOT [-I ../Build_Deps/Build_Deps.pkg.tar.zst]
  • Unmount
    # umount $CHROOT /mnt/chroots/tmp

Sed

The usage of group in regular expression:

Exchange the first column and second column

$ sed -r 's/^([0-9]*)([\t ]*)([^\t ]*)/\3\2\1/' data.txt

Note: The numbering of the groups depend on the appear order of the left parentheses (:

(( )( )( ))
12  3  4

Delete the line start by std: sed -r '/^std/d' main.txt

Rsync

  1. Copy and preserve all attributes
    $ rsync -aP $SOURCE_DIR/ $TARGET_DIR/`
  2. Copy only, don't keep permission and owner (keep only touch times)
    $ rsync -rltP --no-owner --no-group --no-perms $SOURCE_DIR/ $TARGET_DIR/
  3. Synchronize folders remotely, 
    $ rsync -azP -zc=zstd --exclude={"filename1","path/to/filename2"} \
--delete $SOURCE_DIR/ $TARGET_DIR/

Arguments explanation:

  • -a, --archive: Equivalent to -rlptgoD. It's a quick way of saying you want recursion and want to preserve almost everything.
  • -r, --recursive: Copy directories recursively.
  • -l, --links: Add symlinks to the transferred files instead of noisily ignoring them with a "non-regular file" warning for each symlink encountered.
  • -p, --perms: Preserve permissions.
  • -t, --times: Preserve modification times.
  • -g, --group: Preserve group.
  • -o, --owner: Preserve owner (super-user only).
  • -D: Same as --devices --specials.
  • --devices: Transfer character and block device files to the remote system to recreate these devices (Super-user only).
  • --specials: Transfer special files, such as named sockets and fifos.
  • -P: Same as --partial --progress.
  • --partial: Keep partially transferred files. By default, rsync will delete any partially transferred file if the transfer is interrupted.
  • --progress: Show progress during transfer.
  • -z, --compress: Compress file data during the transfer.
  • -zc=STR, --compress-choice=STR: Choose the compression algorithm
  • --delete: Delete extraneous files from destination directories.

Iproute2

ss

Another utility to investigate sockets

List sockets statistics: ss -s

See which process was using specific UDP port:

# ss -lnptu | grep $PORT_NUMBER

Arguments explanation:

  • -l, --listening: Display only listening sockets (these are omitted by default).
  • -n, --numeric: Do not try to resolve service names.
  • -p, --processes: Show process using socket.
  • -t, --tcp: Display TCP sockets
  • -u, --udp: Display UDP sockets.

chmod directories only (exclude files)

Recursively give directories read & execute privileges:

# find /path/to/dir -type d -exec chmod 755 {} \+

Recursively give files read privileges:

# find /path/to/dir -type f -exec chmod 644 {} \+

Bluetooth Dual Boot Pairing

Extracting on Linux

# cryptsetup open --type=bitlk /dev/nvme0n1p3 win11 <<<XXXXXX-XXXXXX-XXXXXX-XXXXXX-XXXXXX-XXXXXX-XXXXXX-XXXXXX
# mount -t ntfs3 /dev/mapper/win11 /mnt/win11
$ cd /mnt/win11/Windows/System32/config
# chntpw -e SYSTEM
> cd ControlSet001\Services\BTHPORT\Parameters\Keys
> ls
Node has 1 subkeys and 0 values
  key name
  <xxxxxxxxxxxx>
> cd xxxxxxxxxxxx
> ls
Node has 1 subkeys and 4 values
  key name
  <d1350d003eee>
  size     type              value name             [value if type DWORD]
    16  3 REG_BINARY         <CentralIRK>
    16  3 REG_BINARY         <aaaaaaaaaaaa>
    16  3 REG_BINARY         <bbbbbbbbbbbb>
    16  3 REG_BINARY         <cccccccccccc>
> hex aaaaaaaaaaaa # For < Bluetooth 5.1 devices
> cd aaaaaaaaaaaa # For Bluetooth 5.1 devices
> hex LTK
> hex ERand
> hex EDIV
> hex IRK

Useful python snippets

>>> LTK='<hex-of-LTK>'.replace(' ', '')
>>> ERand=int(''.join(list(reversed('<hex-of-ERand>'.strip().split()))), 16)
>>> EDIV=int(''.join(list(reversed('<hex-of-EDIV>'.strip().split()))), 16)
>>> IRK=list(reversed('<hex-of-IRK>'.strip().split()))
>>> print('LTK: ', LTK, '\n', 'ERand: ', ERand, '\n', 'EDIV: ', EDIV, '\n', 'IRK: ', ''.join(IRK))

Kernel interface

UUID Generator (Or uuidgen):

$ cat /proc/sys/kernel/random/uuid

Show battery capacity remain:

$ cat /sys/class/power_supply/<Your battery name>/capacity

List network interfaces:

$ ls /sys/class/net # Or
$ ip link

List monitor modes from kernel DRM module

$ cat /sys/class/drm/card1/card1-eDP-1/modes

Show current module's parameters:

# cat /sys/module/nvidia_drm/parameters/modeset

Inform the OS of partition table changes

# partprobe

D-Bus

Manually inhibit / pause clightAUR.

Show all properties:

$ busctl --user introspect org.clight.clight /org/clight/clight org.clight.clight

Call method Inhibit:

$ busctl --user call org.clight.clight /org/clight/clight org.clight/clight Inhibit b true

Check property Inhibited:

$ busctl --user get-property org.clight.clight /org/clight/clight org.clight.clight Inhibited

Call method Pause:

$ busctl --user call org.clight.clight /org/clight/clight org.clight.clight Pause b true

Check property Suspended:

$ busctl --user get-property org.clight.clight /org/clight/clight org.clight.clight Suspended

SSH

Stop a remote control connection:

$ ssh -O stop proteus@proteusdesktop

ssh-keygen

Show the fingerprint of a keyfile:

$ ssh-keygen -l -f </path/to/key>
$ ssh-keygen -l -E md5 -f </path/to/key>

Modify the comment of a keyfile:

 $ ssh-keygen -c -C <Your comment> -f </path/to/key>

Show the information of a keyfile:

$ ssh-keygen -y -f <Your key>

Regenerate host keys:

# rm /etc/ssh/ssh_host_*
# ssh-keygen -A

SSH Tunnel

X11vnc startup with SDDM and SSH Tunnel:

ssh -t -L 5900:localhost:5900 <REMOTE HOST> 'sudo x11vnc -localhost -display :0 -auth $(find /var/run/sddm/ -type f)'

GPU Environment Variables

# /usr/share/glvnd/egl_vendor.d/*
__EGL_VENDOR_LIBRARY_FILENAMES='/usr/share/glvnd/egl_vendor.d/10_nvidia.json'
__GLX_VENDOR_LIBRARY_NAME=nvidia
# /usr/share/vulkan/icd.d/*
VK_ICD_FILENAMES='/usr/share/vulkan/icd.d/nvidia_icd.json'

# lspci -D | grep VGA
DRI_PRIME=pci-0000_06_00_0 glxinfo | grep 'OpenGL renderer'

# /usr/lib/dri/*_dri.so
MESA_LOADER_DRIVER_OVERRIDE=iris

# /usr/lib/dri/*_drv_video.so
LIBVA_DRIVER_NAME=

LIBVA_DRIVER_NAME=radeonsi vainfo --display drm --device /

certbot

Register a wildcard domain hosted on Cloudflare

# certbot certonly --dns-cloudflare --dns-cloudflare-credentials \
~/.secrets/cloudflare.ini \
--server https://acme-v02.api.letsencrypt.org/directory \
--email <EMAIL> --agree-tos --no-eff-email -d '*.proteus.net'

Adjust brightness of a monitor supports DDC

ddcutil -l C340SCA getvcp 10
ddcutil -l C340SCA setvcp 10 - 5

GnuPG

Issue: "There is no assurance this key belongs to the named user" Solution: Set the trust level of the keys:

gpg --edit-key
gpg> trust
Your decision? 5
gpg> quit

Git

Show pretty commit history

git -P log \
--pretty='format:%C(auto)%G?%d %h %an %ar %s' \
--graph --all --color=always | less

BIND

rndc

Generate a key

$ tsig-keygen -a hmac-sha384 custom
key "custom" {
  algorithm hmac-sha384;
  secret "oGJ8/z7ynKx2nzEf7DQxnBypbsIDivrp4qzcUT9EkEE=";
};

rndc reconfig
rndc status
rndc dnssec -status tailba6c3f.ts.net

DNSSEC

The new dnssec-policy let the keys under nameds control. In principle the keys become more like dynamic zone data than static configuration.

Get DS record from the key

$ dnssec-dsfromkey Ktailba6c3f.ts.net.+015+50543.key
tailba6c3f.ts.net. IN DS 50543 15 2 80F61B4AF40FCFF8A61852F5479C299BD31676F5F65765AE3AEDA08C9B3C78A0

In this example, 15 represents ED25519, and 2 represents the digest type SHA-256, the key ID is 50543.

Print key's metadata:

$ dnssec-settime -p all Ktailba6c3f.ts.net.+015+50543

The CDS and CDNSKEY are identical to the DS and DNSKEY records, but they automate the process to pass the records to the parent zone.

yt-dlp

List all available formats for a video:

$ yt-dlp --cookies-from-browser firefox -F 'https://www.youtube.com/watch?v=S5bfdUTrKLM&t=3s'

Download with specific format code

$ yt-dlp --cookies-from-browser firefox -f 'bestvideo*+bestaudio/best'
  • -f, --format Use -f - for interactive selector (implies -F);
  • -F, --list-formats List available formats of each video;
  • --audio-multistreams Allow multiple audio streams to be merged into a single file;
  • --video-multistreams Allow multiple video streams to be merged into a single file.

Format Selection:

  • b*, best*: Select the best quality format that contains either a video or an audio or both (i.e.; vcodec!=none or acodec!=none).
  • b, best: Select the best quality format that contains both video and audio. Equivalent to best*[vcodec!=none][acodec!=none].
  • /: Or logic.

mdadm FakeRAID

Erase the metadata:

# mdadm --zero-superblock /dev/nvme0n1p2

Stop the array:

# mdadm --stop /dev/md127

nvmecli

Get LBA format:

# sudo nvme id-ns /dev/nvme0n1 -H | grep 'LBA Format'

Warning: Most SSDs use a 4096 byte physical sector size, even though some report 512.

keepassxc-cli

Generate a password that has 14 length, upper and lowercases, numeric, specials:

keepassxc-cli generate -L14 -lUns

SSSD

  • Show domain status
    sudo sssctl domain-list
sudo sssctl domain-status 'LDAP'
  • Check a user's authentication
    sudo sssctl user-checks proteus -a auth -s sudo # Any modules in /etc/pam.d
  • Expire all cache
    sudo sssctl cache-expire -E
  • Verify a remote user/group
    getent passwd proteus@ldap
getent group proteus@ldap

Obsoleted

pwgen

Random password generator

e.g. Generate 20 different passwords which has length 12 and at least one big letter (-c), number (-n), symbol (-y). Furthermore, -s can generate more randomize passwords

$ pwgen -cnys 12 20

Iptables

  1. IPSET u32 match Check whether the last value of TCP Seq in a network package equals 41 : 0>>22&0x3C@ 4 &0xFF=0x29 Example (Use Wireshark to catch packages), have this IP header:

    Source IP: 121.41.89.52
= 01111001 00101001 01011001 00110100B = 79 29 59 34H = 2032752948D
IP Header：
45 00 00 3c 00 00 40 00 31 06 ef 34 **79 29 59 34** c0 a8 c7 81
TCP Header：
00 50 95 3c 8d 7f 52 ac 69 15 33 be a0 12 71 20 cd dc 00 00 02 04 05 14 04 02 08 0a 08 c8 62 fa 00 1c 30 a1 01 03 03 07

    0: Start from offset 0, get 4 bytes (since u32 means 32 bits). Here is 45 00 00 3c. >>22 shift right 22 bits. So 45 00 00 3c = 0100 0101 0000 0000 0000 0000 0011 1100 becomes 1 14 = 01 0001 0100. &0x3C do bitwise AND with 0x3C (like a filter). Then

     01 0001 0100
& 00 0011 1100
--------------
 00 0001 0100
`

    Conclusion, 0>>22&0x3C get the 4–7 bits from the IP header.

    So the length of this IP header is 01 0100 = 20D.

    @ offset the pointer with the value on the left. So 0>>22&0x3C@ gets 20 bytes forward from the start address. We want to know the TTL value of this TCP packet. So get value from TCP header at index of 4 and filter it using mask 0xFF to get last 1 byte (8 bits). Finally, compares to0x29 = 41D

    It can also compare to a range. e.g. Whether between 41-60: 0>>22&0x3C@ 4 &0xFF=0x29:0x3C

Matlab

# matlab.desktop
Name=Matlab2022b
Comment=A high-level language for numerical computation and visualization
GenericName=Matlab
Exec=env _JAVA_AWT_WM_NONREPARENTING=1 LD_PRELOAD=/usr/lib/libstdc++.so LD_LIBRARY_PATH=/usr/lib/xorg/modules/drivers/ MESA_LOADER_DRIVER_OVERRIDE=iris /home/proteus/MATLAB/R2022b/bin/matlab -desktop
Categories=Education
Type=Application

// java.opts
-Djpgl.disable.openglarbcontext=1

References

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