Missing Semester

MetaProgramming

Programming Workflow

Build System

run commands for you and reslove dependencies

Make

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$ make
make: *** No targets specified and no makefile found.  Stop.

Makefile

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paper.pdf: paper.tex plot-data.png
	pdflatex paper.tex

plot-%.png: plot.py %.dat
	./plot.py -i $*.dat -o $@

Special variables

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$@ // the name of the target
% //The % in a rule is a “pattern”, and will match the same string on the left and on the right. (like .* in regex)
$* // result of match

Version number(Semantic versioning)

usually they are three numbers separated by dot

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$ python3 --version
Python 3.9.7
$ python2 --version
Python 2.7.16
$ bash --version
GNU bash, version 3.2.57(1)-release
....

x.x.x

Major.Minor.Patch

  • Patch : no interface change
  • Minor : new features added (backwards compatible)
  • Major : backwards incompatible changes(some thing deleted)

Continuous Integration(CI)

Event driven system, automatically do something for you when you take some action

wiki

Daemon Processes

wiki

background programs, name ended with ‘d’, aka services

For example

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$ ps -A | grep -e 'd$'
    1 ?        00:00:00 systemd
    2 ?        00:00:00 kthreadd
    8 ?        00:00:00 rcu_sched
   16 ?        00:00:00 kauditd
   17 ?        00:00:00 khungtaskd
   21 ?        00:00:00 ksmd
   22 ?        00:00:00 khugepaged
   24 ?        00:00:00 kintegrityd
   25 ?        00:00:00 kblockd
   27 ?        00:00:00 md
   30 ?        00:00:00 watchdogd
   78 ?        00:00:00 kthrotld
  447 ?        00:00:00 systemd-udevd
  450 ?        00:00:00 lvmetad
  453 ?        00:00:00 rpciod
  454 ?        00:00:00 xprtiod
  486 ?        00:00:00 rpcbind
  648 ?        00:00:00 atd
  670 ?        00:00:00 systemd-logind
  689 ?        00:00:00 rsyslogd
  706 ?        00:00:00 polkitd
  954 ?        00:00:00 sshd
 1801 ?        00:00:00 sshd
 1803 ?        00:00:00 systemd
 1891 ?        00:00:00 sshd

You can configure your own daemon program (called system unit)with a config file and systemd will manage it for you.

Say you want to start clash after boot up your computer

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$ cd /etc/systemd/system
$ touch clash.service
$ cat clash.service
[Unit]
Description=Clash Proxy
After=network.target

[Service]
User=vagrant
Group=vagrant
WorkingDirectory=/home/vagrant
ExecStart=/usr/bin/clash
Restart=on-failure

[Install]
WantedBy=multi-user.target
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$ systemctl daemon-reload
$ systemctl enable clash.service
$ systemctl start clash.service
$ systemctl status clash.service

If you want to schedule some tasks by time, cron is the daemon already there for you

You can “Query or send control commands to the systemd manager.” via systemctl.
See more at systemctl --help

simple tutorial

FUSE

Filesystem in User Space

wiki