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Cheatsheet

Python

  • f'{0x0c180606:032b}'

VNC

  • Server side: Start server on certain port with certain geometry: 

    vncserver :66 -geometry 1920x1080

  • Client side: for safety, use SSH tunnel.

    • -p 22: ssh port is 22
    • -L 7777:localhost:5966: Forward localhost’s 7777 to server’s 5966 
      Step 1)
ssh -p 22 -v -C -L 7777:localhost:5966 root@yourserver.com

Step 2)
Use VNC client to establish connection with localhost:7777

virsh

  • Pass commands to QEMU in the virsh bash: 
    # qemu-monitor-command guest_os_id --hmp "info cpus"

Markdown

tmux

bash

  • Show current git branch in PS1: 

    parse_git_branch() {
     git branch 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/ git:(\1)/'
}

PS1="\[\e[32m\][\u@\h: \W\e[33m\]\$(parse_git_branch)\[\033[32m\]]\[\e[00m\] $ "

  • Forward man pages to vim: 

    vman() { man $* | col -b | vim -c 'set ft=man nomod nolist' -; }    
alias man="vman"

Git

git log --pretty="%C(Yellow)%h %C(auto)%d (%C(Green)%cr%C(reset))%x09 %C(Cyan)%an: %C(reset)%s" --date=short --graph

QEMU

  • Run standalone kernel: 
    # Create a new directory to store the serial output from printk().
OUTPUT_DIR="test-output"
if [ -e $OUTPUT_DIR ]; then
        if [ -f $OUTPUT_DIR ]; then
                echo "ERROR: $OUTPUT_DIR is not a directly"
                exit 1
        fi
else
        mkdir -p $OUTPUT_DIR
fi

KERNEL="arch/x86_64/boot/bzImage"
KERNEL_PARAM="console=ttyS0 earlyprintk=serial,ttyS0,115200"
SERIAL="-serial file:$OUTPUT_DIR/ttyS0 -serial file:$OUTPUT_DIR/ttyS1"

# -cpu Haswell,+tsc,+sse,+xsave,+aes,+avx,+erms,+pdpe1gb,+pge \
# Above -cpu option may not work with some kernels.
qemu-system-x86_64 -s  \
        -nographic \
        -kernel $KERNEL -append "$KERNEL_PARAM" \
        -no-reboot \
        -d int,cpu_reset -D $OUTPUT_DIR/qemu.log \
        $SERIAL \
        -m 16G \
        -monitor stdio \
        -smp cpus=24,cores=12,threads=2,sockets=2 \
        -numa node,cpus=0-11,mem=8G,nodeid=0 \
        -numa node,cpus=12-23,mem=8G,nodeid=1

Install CentOS on Dell PowerEdge

  • Enable SR-IOV for future usage
    • Press F11 Boot Manager during boot
    • Find Integrated Devices
    • Enable SR-IOV Global Enable
  • Partition
    • /boot: e.g, 50GB
    • swap: e.g, 4G
    • /: all left
  • Don’t forget to enable Network during installation.
  • Change SSH port
    • Disable firewalld
      • systemctl stop firewalld
      • systemctl disable firewalld
    • If SELinux is enabled
      • yum install policycoreutils-python
      • semanage port -a -t ssh_port_t -p tcp #PORTNUMBER
    • Change /etc/ssh/sshd_config
    • systemctl restart sshd

Avoid Typing SSH Password

  • Generate keys: ssh-keygen -t rsa
  • Copy to remote: ssh-copy-id -i ~/.ssh/id_rsa.pub username@remotehost -p 22

GRUB2 on Ubuntu

  • Nothing like grubby?! Shame on you.
  • Step I: cat /boot/grub/grub.cfg | grep menuentry 
    menuentry 'Ubuntu, with Linux 4.16.0' --class ubuntu  ...
menuentry 'Ubuntu, with Linux 4.9.92' --class ubuntu  ...
  • Step II: Open /etc/default/grub, change
    • GRUB_DEFAULT=”Advanced options for Ubuntu>Ubuntu, with Linux 4.16.0”
    • GRUB_DEFAULT=”Advanced options for Ubuntu>Ubuntu, with Linux 4.9.92”
  • Step III: sudo update-grub

Migrate to Ubuntu From MacOS