Miscellanea 2021

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2021/01/04

  • GoCD, the CI/CD tool like Jenkins

2021/01/17

  • !<command prefix letter> will rerun the last command that starts with this prefix.

2021/01/23

  • runbook/playbook is for commonly problems solution and instruction.

2021/01/25

  • pipeline echo 123 |& cat, |& means piping message to both stdout and stderr.

2021/01/27

  • envsubst command: substitutes environment variables in shell format strings.

2021/04/03

  • yq, similar with jq command but for yaml parsing.

2021/05/11

  • ps -o etime -o time -p <pid>, show process the elapsed time since it started, and the cpu time.

2021/09/05

  • docker container run is the same as docker run
  • docker container run = docker container create + docker container start + [docker container attach]

2021/10/06

  • Docker has OS or not? , obviously no, remember docker vs virtual machine. Docker is lightweight virtualization, For Linux docker, the container always runs/shares on linux/host kernel, docker image supplies the necessary files, libs, utilities, etc.

  • We have ubuntu, centos, alpine docker image, they can run in the same host OS, the key differences are filesystem/libraries, they share the host OS kernel. see this post, also see the second answer: “Since the core kernel is common technology, the system calls are expected to be compatible even when the call is made from an Ubuntu user space code to a Redhat kernel code. This compatibility make it possible to share the kernel across containers which may all have different base OS images.”

  • Docker run on MacOS, Docker on Mac actually creates a Linux VM by LinuxKit and containers run on it.

2021/10/31

  • DNS record type TXT and A: TXT is for owner custom info, A is IP hostname mapping.

2021/12/25

  • Why ls -l does not show group name: because of alias alias ls="ls -G", -G will suppress the group name in long format, using /bin/ls -l instead.
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