Posted Updated computer25 minutes read (About 3745 words)

linux-usage

A manual of my Linux gists

Linux Common Commands

Reset User faillocks

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$ faillock --user <username> --reset

Binary File Editing

Generate hexdump:

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$ xxd TIAS2781RCA4.bin > TIAS2781RCA4.bin.txt

Revert plaintext hexdump back into binary:

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

PDF Editing

PDF Extracting:

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$ pdfimages --all in.pdf out_dir/

PDF Regenerate:

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$ 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

Steam

Launch Heart of Iron IV (With FSR1, VRR, MangoHud)

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$ 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%

Libvirt

Use --print-xml | less to see generated xml only for debugging.

  • Install a Arm Cortex-a53 machine
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    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
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    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:

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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 & private key (optional, can use CA’s key):

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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 request with CA certificate:

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openssl x509 -CA ca.pem -CAkey ca.key.pem -CAcreateserial -extfile <(printf "subjectAltName = DNS:localhost,DNS:*.tailba6c3f.ts.net\nauthorityKeyIdentifier = keyid,issuer\nbasicConstraints = CA:FALSE\nkeyUsage = digitalSignature, keyEncipherment\nextendedKeyUsage=serverAuth") -req -in server.csr.pem -sha384 -out server.pem
````
> `-CAcreateserial` will generate `ca.srl`, afterwards using `-CAserial ca.srl`.

Show information:
```console
openssl openssl ec -text -noout -in server.key.pem
openssl req -text -verify -in server.csr.pem
openssl x509 -noout -text -in server.pem

Shell builtin & Concept

  • Shortcut:
    <M-b/f> Move back / forward a word.
    <C-b/f> Move back / forward a char.
    <C-s> Pause STDOUT.
    <C-q> resume STDOUT.
    <C-r> Enter history search mode.
    <C-g> Beaak out a newline; Leave history search mode.
    <M-h> Open manual for current typed command.

  • filter: Programs that can be used in shell pipe.
    What programs can be used in shell pipe? Programs that process stdin line-by-line, then output results to stdout.
    E.G. cp, diff are NOT belong to filter

  • Linux Shell Features

    • If no argument, default read from stdin.
    • Default output into stdout

  • type xxx Show command type (builtin or outer)

  • man builtins Show manual of shell builtins.

  • help xxx Fast help for shell builtin xxx.

  • history Show shell history, which can be used along with fc.

Redirect:

  • Write (Override) Output redirect >

  • Append output redirect >>

  • Input redirect (Strings) <<<

  • How to process shell args and stdin, stdout, stderr:

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    #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) {
      if (c >= 'a' && c <= 'z')
        c = c + 'A' - 'a';
      fputc(c, stdout);
      c = fgetc(stdin);
     }
     fflush(stdout);
     fprintf(stderr, "I am stderr\n");
     fflush(stderr);
    }

  • $$ (equivalent to ${$}) is current shell’s PID.
    Variables in shell default to string.
    Shell treat all string type as zero if do arithmetic to them.
    declare -i defines integer variable

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    $ x=5
    $ y=3
    $ declare -i l=$x+$y
    $ l=l+3 // Integer variable can do arithmetic directly
    $ k=$(($x+$y)) // do arithmetic but the type of 'k' still remains string

    declare +i removes integer attribute of the variable.

  • Shell For loop

    for.sh
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    for ((i=0;i<10; i=i+1)); do
      echo $i
    done

    for i in {1..10}; do
      echo $i
    done

    # Step = 2
    for i in {1..10..2}; do
      echo $i
    done

  • Shell Function

    sum.sh
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    function sum() {
       echo $# # The numeber of parameters
       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 array type
    }

    sum 1 2 7 'a'
    # Result:
    # 4
    # 1 2 7 a
    # ./sum.sh
    # 1
    # 1 2 7 a

  • awk
    To filter only the column 3 with value >= 90: awk '$3 >= 90 { print }',
    where $3 >= 90 is pattern (Optional), print is the action.
    $0 means whole line.
    NR means 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 support variables, To calculate sum awk 'BEGIN { sum = 0 } { sum = sum + $3 } END { avg = sum / NR; print NR, sum, avg }'
    e.g. To do char count awk '{ cc = cc + length($0) + 1 } END { print NR, wc }' (Validate by wc -ml. The extra +1 because there is \n at each end of line)
    NF means mean word count of current line. e.g. Do word counts awk '{ cc = cc + length($0) + 1; wc = wc + NF } END {print NR, cc, wc }' (Validate by wc)
    -F set the delimiter awk -F':'

  • egrep -o show only contents that matched, e.g. To show the order number only: cat */*.txt | egrep '^[0-9-]+' -o | sort | less
    -n show line nunber, -v reverse mathch, -i case insensitive, -r search directories recursively.

  • sort default to ASCII code sort, for nunberic sort, use parameter -n.
    e.g. Sort the third column of scores.txt: sort -n -k 3 scores.txt | less
    -r do reverse sort.
    -u remove duplicates. The difference to sort | uniq is uniq removes exactly same content line, while sort -u remove lines which has the same match.

  • tr do uppercase / lowercase. e.g. tr 'a-z' 'A-Z' (equivalent to tr '[:lower:]' '[:upper:]')

  • xargs format stdin as parameters to the command.
    e.g. To 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’s format explanation:
    Three actions: d(elete), c(hange), a(dd)
    e.g. 130d129 delete line 130 and then align to line 129; 249a130,131 add later’s line 130, 131 to former’s line 249; 271,373c163,271 replace later’s line 163, 271 to former’s line 271, 373.

  • nohup prevents program to hang on session terminate. e.g. nohup bash run0.sh &

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

DSDT (Differentiated System Description Table)

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

Extract & Modify DSDT

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$ # 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 hex AML table (in C) dsdt.aml
$ iasl -tc dsdt.dsl | grep Errors

Extract & Modify SSDT

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$ # Modify SSDT (System Service Descriptor Table)
# for i in /sys/firmware/acpi/tables/SSDT*; do \
    cat $i > ${i##*/}; \
done
$ iasl -d SSDT*
$ rg "SB.PCI0.GPP8.NVME" SSDT*.dsl
$ # Found keywords in SSDT14.dsl, comment out it
$ vim SSDT14.dsl
$ # Compile SSDT to generate SSDT14.aml
$ iasl -tc SSDT14.dsl
$ # Create a CPIO archive
$ mkdir -p kernel/firmware/acpi
$ # through dsdt.aml is optional if it keep untouched
$ cp dsdt.aml SSDT14.aml kernel/firmware/acpi
$ find kernel | cpio -o -H newc > SSDT14

To extract CPIO archive

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

Inkscape

  1. Node Tool
  • Dragging over line with <M> to select their nodes, release to switch to rubberband mode.
  • ! inverts node selection in current subpath(s).
  • [,] rotate 15° <,> scale.
  • 2x<LMB> or <C-M-LMB>: Add node.
  • 2x<LMB> or <C-M-LMB> or <Del>: Delete node. Use <C-Del> if you don’t wanna Inkscape to preserve the shape.
  • <S>-d duplicate selected nodes, <S>-b breaks selected nodes, <S>-j joins two selected endnodes.
  • <S>-c mades node cusp, which means its two handles can move independently at any angle, to each other.
    <S>-s mades node smooth, which means its handles are always colinear.
    <S>-y mades node symmetric, which is same as smooth, but the handles also have the same length.
    <S>-a mades node auto-smooth, which is a special node that automatically adjusts the handles of the node and surrounding auto-smooth nodes to maintain a smooth curve.

    When switching the type of node, preseve one position of the two handles by hovering cursor over it. So that only the other handle is rotated / scaled to match.

  • <C-LMB>: Retract handle.
    <S-LMB>: Pull out handle.
    <C>-k: Combine into compound path.
    <C-S>-k: Break apart compound path.
  • Compound path is not the same as a group. It’s a single object which is only selectable as a whole.
  • Parts of a path (i.e. a selection of nodes) can also be copied with <C>-c and inserted as a new path with <C>-v.
  • <C-S>-c: Convert shape or text to path.
  • Boolean Operators
    Union <C>-+; Difference <C>--(Bottom minus top); Intersection <C>-*;
    Exclusion <C>-^; Division <C>-/; Cut Path <C-M>-/.

    Exclusion command looks similar to Combine, but it is different in that Exclusion adds extra nodes where the original paths intersect.
    The difference between Division and Cut Path is that the former cuts the entire buttom object by the path of the top object, while the latter only cuts the bottom object’s stroke and removes any fill.

  • Common use cases
    Split Path: <C-S-M>-k splits non-connected sections of a path.
    Fracture: <S-M>-f fractures connected paths piece by piece.
    Flatten: <S>-f, new difference that remove all overlapped areas in the selected paths.
  • Shape Build Tool (X)
    Before switch to the tool, select at least one overlapping object.
    <LMB> to add a section to the result;
    <S-LMB> to removee it (it can be used to create a hole in it’s place).
    <LMB>-Drag to connect multiple sections to one.
    <S-LMB>-Drag to remove a contiguous section.
  • Inset and Outset
    Inkscape can expand and contract shapes not only by scaling, but also by offsetting an object’s path, i.e. by displacing perpendicular to the path in each point.
    <C>-( Inset; <C>-) Outset.
    <C>-j Dynamic Offset (create an object with a draggable handle controlling the offset distance).
    <C-M>-i Linked Offset, create a dynamic offset linked to the original path.
  • Simplitication
    <C>-l: Simplify. This may be useful for paths created by the Pencil tool. The amount of simplication depends on the size of the selesction. Moreover, the simply command is accelerated if press <C>-l several times in quick succession.
  1. Pen Tool (B)
  • <LMB> creates a sharp node.
  • <LMB>-Drag creates a smooth Bezier node.
  • <S> while dragging out a handle.
  • <C> limits the direction of either the current line segment or the Bezier handles to 15 ° increments.
  • <CR> finalizes the line; <Esc> cancels it.
  1. Text Tool
    <C-S>-t: Open the Text and Font dialog.
    <M>-<,>: Decrease, Increase the letter spacing of a text object. <C-M>-<,> adjust line spacing in multi-line text objects.
    <M-Left,Right,Up,Down>: Kerning the letters right of the cursor horizontally, vertically.
    <LMB>-Drag: Click and drag with the text tool.
  2. XML Editor
    <C-S>-x: Allows to do tricks.

Filesystem

  1. A file corresponds to one inode (which stores the file properties and the pointer table of blocks) and ordered number 0~n blocks (stores the data of the file).
  2. Hard symbol links: Same file but has multiple names; Only apply to file, does not support directory; Can’t across filesystems.
    Soft symbol links: Different file but same name; Could apply to file or directory; Can across filesystems.
  3. Why directories could not 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.
  • # systool -v -m module_name list options that are set for a loaded module.

Clean Build

  • Prepare
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    $ RAMDISK_SIZE=20
    $ sudo mount --mkdir -t tmpfs -o defaults,size=${RAMDISK_SIZE}G tmpfs /mnt/chroots/tmp
    $ sudo dd if=/dev/zero of=/mnt/chroots/tmp/ramdisk status=progress bs=128K count=$(($RAMDISK_SIZE*8192))
    $ sudo mkfs.btrfs -n 8k -m single -f /mnt/chroots/tmp/ramdisk
    $ sudo mount --mkdir -t btrfs -o loop,sync,compress=zstd /mnt/chroots/tmp/ramdisk /mnt/chroots/arch
    $ CHROOT=/mnt/chroots/arch
  • Use paru
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    $ paru -S --chroot=/mnt/chroots/arch <Packages>
  • Manual Way
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    $ mkarchroot $CHROOT/root base-devel
    $ makechrootpkg -c -r $CHROOT [-I ../Build_Deps/Build_Deps.pkg.tar.zst]
  • Umount
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    sudo umount $CHROOT /mnt/chroots/tmp

Sed

The usage of group in regular expression: ((regex) and \1)

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$ sed -i 's,\$\([^$]*\)\$,\\\\(\1\\\\),g' file.md

grep

Find in files:

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$ grep -iRl "your-text-to-find" ./

rsync

  1. Copy and preserve all attributes
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    $ rsync -aXHAv -P $SOURCE_DIR/ $TARGET_DIR/`
  2. Copy only, don’t keep permission and owner (keep only touch times)
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    $ rsync -rlt -P --no-owner --no-group --no-perms $SOURCE_DIR/ $TARGET_DIR/
  3. Synchronize folders, be aware that --delete will delete any additional folder / files from $TARGET_DIR which is not in $SOURCE_DIR
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    $ rsync -aXHAz -v -P --exclude={"filename1","path/to/filename2"} --delete $SOURCE_DIR/ $TARGET_DIR/

ss

ss is member of iproute tools set

List sockets statitics: ss -s
To see which process was using specific port: ss -nlptu | grep $PORT_NUMBER

dd

To backup your GPT:

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

To restore your GPT

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

pwgen

Random password generator
To generate 20 different passwords which has length 12 and at least one big letter (-c), number (-n), symbol (-y). Furthmore, -s can generate more randomize passwords

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$ pwgen -cnys 12 20

chmod directories only (exclude files)

To recursively give directories read & execute privileges:

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

To recursively give files read privileges:

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

Reference from StackExchange

Exclusive delete

Enable glob extension

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

Bluetooth dual boot pairing

Extracting on Linux

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# cryptsetup open --type=bitlk /dev/nvme0n1p3 win11 <<<XXXXXX-XXXXXX-XXXXXX-XXXXXX-XXXXXX-XXXXXX-XXXXXX-XXXXXX
# mount /dev/mapper/win11 /mnt/win11
$ cd /mnt/Windows/System32/config
$ chntpw -e SYSTEM
> cd ControlSet001\Services\BTHPORT\Parameters\Keys
> cd xxxxxxxxxxxx
> hex xxxxxxxxxxxx # For < Bluetooth 5.1 devices
> cd xxxxxxxxxxxx # For Bluetooth 5.1 devices
> hex LTK
> hex ERand
> hex EDIV
> hex IRK

Useful python snippets

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$ python
>>> 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))

ssh-keygen

  1. Show the fingerprint of a keyfile:
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    $ ssh-keygen -l -f </path/to/key>
    $ ssh-keygen -l -E md5 -f </path/to/key>
  2. Modify the comment of a keyfile:
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    $ ssh-keygen -c -C <Your comment> -f </path/to/key>
  3. Show the information of a keyfile:
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    $ ssh-keygen -y -f <Your key>

Kernel interface

  1. UUID Generator (Or uuidgen):
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    $ cat /proc/sys/kernel/random/uuid
  2. Show battery capacity remain:
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    $ cat /sys/class/power_supply/<Your battery name>/capacity
  3. List network interfaces: ls /sys/class/net or ip link
  4. Show monitor modes from kernel DRM module
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    $ cat /sys/class/drm/card1/card1-eDP-1/modes
  5. (D-Bus) Manually inhibit / pause clightiAUR.
    Check all
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    $ busctl --user introspect org.clight.clight /org/clight/clight org.clight.clight
    Call method Inhibit
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    $ busctl --user call org.clight.clight /org/clight/clight org.clight/clight Inhibit b true
    Check property Inhibited
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    $ busctl --user get-property org.clight.clight /org/clight/clight org.clight.clight Inhibited
    Or call method Pause
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    $ busctl --user call org.clight.clight /org/clight/clight org.clight.clight Pause b true
    Check property Suspended
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    $ busctl --user get-property org.clight.clight /org/clight/clight org.clight.clight Suspended
  6. Show current modules paraeter
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# cat /sys/module/nvidia_drm/parameters/modeset

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:
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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

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

## bash

### IF Statement in Bash

- Integer Operator
  ```plaintext
  -eq    equal
  -ne    not equal
  -gt    greater
  -ge    geeater or equal
  -lt    lesser
  -le    lesser or equal
  • File Operator
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    -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
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    ==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
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    -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
::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"
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 substitition, single / means non-greedy
echo ${STR//o/b} # /path/tb/fbb.cpp Two / is greedy

Bash Built-in variables

$# number of arguments

SSH Tunnel

X11vnc startup with SDDM and SSH Tunnel.
Please be aware that this command need to be executed on client-side.

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

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)

GPU Environment Variables

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# /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 /

Matlab

matlab.desktop
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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
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-Djpgl.disable.openglarbcontext=1

Certbot

Register a wildcard domain hosted on Cloudflare

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# 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 '*.ndoskrnl.net'

linux-usage

https://magic0whi.github.io/linux-usage/

Author

Proteus Chan

Posted on

2020-02-08

Updated on

2024-08-17

Licensed under

Categories

Tags

electronic-and-information-engineering1
mathematics5
postgraduate2
senior-high-schoool1
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