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#353 GNU/Linux 上如何快速创建一个大文件？「from StackOverflow」

Linux 开发工具 2019-12-25

在 StackOverflow 上看到好些种快速创建文件的命令，逐个测试，在 Ubuntu 下可用的方法有以下几种：

time dd if=/dev/zero of=test.img bs=10M iflag=fullblock,count_bytes count=10G
# 0.00s user 0.45s system 1% cpu 39.144 total

# 在 xfsprogs 包中：
# -n 表示不写入数据
time xfs_mkfile -n 10g test.img
# 0.01s user 0.01s system 2% cpu 0.669 total

# 在 VBox 挂载的虚拟磁盘上执行时遇到 “不支持的操作” 错误
# 在 EXT4 磁盘上没有遇到问题，速度很快
time fallocate -l 10G test.img

time truncate -s 10G test.img
# 0.00s user 0.00s system 46% cpu 0.005 total

time dd if=/dev/zero of=test.img bs=1 count=0 seek=10G
# 0.00s user 0.00s system 77% cpu 0.002 total

最后看到的 dd seek 方案深得征信深得朕心。

根据这个思路，Python 创建 10G 的文件应该这么写（也是我一直以来的写法）：

GB = 1 << 30
with open('test.img', 'w') as _file:
    _file.seek(10 * GB - 1)
    _file.write(chr(0))

#352 Systemd 相关命令

Linux Systemd 2019-12-21

apt-file list systemd | grep bin/
systemd: /bin/journalctl
systemd: /bin/loginctl
systemd: /bin/networkctl
systemd: /bin/systemctl
systemd: /bin/systemd
systemd: /bin/systemd-ask-password
systemd: /bin/systemd-escape
systemd: /bin/systemd-inhibit
systemd: /bin/systemd-machine-id-setup
systemd: /bin/systemd-notify
systemd: /bin/systemd-sysext
systemd: /bin/systemd-sysusers
systemd: /bin/systemd-tmpfiles
systemd: /bin/systemd-tty-ask-password-agent
systemd: /usr/bin/bootctl
systemd: /usr/bin/busctl
systemd: /usr/bin/hostnamectl
systemd: /usr/bin/kernel-install
systemd: /usr/bin/localectl
systemd: /usr/bin/resolvectl
systemd: /usr/bin/systemd-analyze
systemd: /usr/bin/systemd-cat
systemd: /usr/bin/systemd-cgls
systemd: /usr/bin/systemd-cgtop
systemd: /usr/bin/systemd-cryptenroll
systemd: /usr/bin/systemd-delta
systemd: /usr/bin/systemd-detect-virt
systemd: /usr/bin/systemd-id128
systemd: /usr/bin/systemd-mount
systemd: /usr/bin/systemd-path
systemd: /usr/bin/systemd-resolve
systemd: /usr/bin/systemd-run
systemd: /usr/bin/systemd-socket-activate
systemd: /usr/bin/systemd-stdio-bridge
systemd: /usr/bin/systemd-umount
systemd: /usr/bin/timedatectl

journalctl
loginctl
networkctl
systemctl
systemd
systemd-ask-password
systemd-escape
systemd-inhibit
systemd-machine-id-setup
systemd-notify
systemd-sysext
systemd-sysusers
systemd-tmpfiles
systemd-tty-ask-password-agent
bootctl
busctl
hostnamectl
kernel-install
localectl
resolvectl
systemd-analyze
systemd-cat
systemd-cgls
systemd-cgtop
systemd-cryptenroll
systemd-delta
systemd-detect-virt
systemd-id128
systemd-mount
systemd-path
systemd-resolve
systemd-run
systemd-socket-activate
systemd-stdio-bridge
systemd-umount
timedatectl

ps -ef | grep -E "systemd|systemd|dns|dhcp|udevd" | grep -Fv grep
root         333       1  0 10:00 ?        00:00:05 /lib/systemd/systemd-journald
root         419       1  0 10:00 ?        00:00:01 /lib/systemd/systemd-udevd
systemd+     546       1  0 10:00 ?        00:00:07 /lib/systemd/systemd-oomd
systemd+     547       1  0 10:00 ?        00:00:00 /lib/systemd/systemd-resolved
systemd+     548       1  0 10:00 ?        00:00:00 /lib/systemd/systemd-timesyncd
message+     573       1  0 10:00 ?        00:00:04 @dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
root         680       1  0 10:00 ?        00:00:00 /lib/systemd/systemd-logind
root         682       1  0 10:00 ?        00:00:00 /usr/sbin/thermald --systemd --dbus-enable --adaptive
markjour     2508       1  0 10:05 ?        00:00:01 /lib/systemd/systemd --user
markjour     2523    2508  0 10:05 ?        00:00:00 /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
markjour     5461    2508  0 10:11 ?        00:00:00 /usr/libexec/gnome-session-binary --systemd-service --session=ubuntu
root        6630       1  0 10:15 ?        00:00:00 systemd-tty-ask-password-agent --wall

#351 Systemd 子命令

Linux Systemd 2019-12-21

Unit Commands:
  list-units [PATTERN...]             List units currently in memory
  list-sockets [PATTERN...]           List socket units currently in memory,
                                      ordered by address
  list-timers [PATTERN...]            List timer units currently in memory,
                                      ordered by next elapse
  is-active PATTERN...                Check whether units are active
  is-failed PATTERN...                Check whether units are failed
  status [PATTERN...|PID...]          Show runtime status of one or more units
  show [PATTERN...|JOB...]            Show properties of one or more
                                      units/jobs or the manager
  cat PATTERN...                      Show files and drop-ins of specified units
  help PATTERN...|PID...              Show manual for one or more units
  list-dependencies [UNIT...]         Recursively show units which are required
                                      or wanted by the units or by which those
                                      units are required or wanted
  start UNIT...                       Start (activate) one or more units
  stop UNIT...                        Stop (deactivate) one or more units
  reload UNIT...                      Reload one or more units
  restart UNIT...                     Start or restart one or more units
  try-restart UNIT...                 Restart one or more units if active
  reload-or-restart UNIT...           Reload one or more units if possible,
                                      otherwise start or restart
  try-reload-or-restart UNIT...       If active, reload one or more units,
                                      if supported, otherwise restart
  isolate UNIT                        Start one unit and stop all others
  kill UNIT...                        Send signal to processes of a unit
  clean UNIT...                       Clean runtime, cache, state, logs or
                                      configuration of unit
  freeze PATTERN...                   Freeze execution of unit processes
  thaw PATTERN...                     Resume execution of a frozen unit
  set-property UNIT PROPERTY=VALUE... Sets one or more properties of a unit
  bind UNIT PATH [PATH]               Bind-mount a path from the host into a
                                      unit's namespace
  mount-image UNIT PATH [PATH [OPTS]] Mount an image from the host into a
                                      unit's namespace
  service-log-level SERVICE [LEVEL]   Get/set logging threshold for service
  service-log-target SERVICE [TARGET] Get/set logging target for service
  reset-failed [PATTERN...]           Reset failed state for all, one, or more
                                      units
Unit File Commands:
  list-unit-files [PATTERN...]        List installed unit files
  enable [UNIT...|PATH...]            Enable one or more unit files
  disable UNIT...                     Disable one or more unit files
  reenable UNIT...                    Reenable one or more unit files
  preset UNIT...                      Enable/disable one or more unit files
                                      based on preset configuration
  preset-all                          Enable/disable all unit files based on
                                      preset configuration
  is-enabled UNIT...                  Check whether unit files are enabled
  mask UNIT...                        Mask one or more units
  unmask UNIT...                      Unmask one or more units
  link PATH...                        Link one or more units files into
                                      the search path
  revert UNIT...                      Revert one or more unit files to vendor
                                      version
  add-wants TARGET UNIT...            Add 'Wants' dependency for the target
                                      on specified one or more units
  add-requires TARGET UNIT...         Add 'Requires' dependency for the target
                                      on specified one or more units
  edit UNIT...                        Edit one or more unit files
  get-default                         Get the name of the default target
  set-default TARGET                  Set the default target

Machine Commands:
  list-machines [PATTERN...]          List local containers and host

Job Commands:
  list-jobs [PATTERN...]              List jobs
  cancel [JOB...]                     Cancel all, one, or more jobs

Environment Commands:
  show-environment                    Dump environment
  set-environment VARIABLE=VALUE...   Set one or more environment variables
  unset-environment VARIABLE...       Unset one or more environment variables
  import-environment VARIABLE...      Import all or some environment variables

Manager State Commands:
  daemon-reload                       Reload systemd manager configuration
  daemon-reexec                       Reexecute systemd manager
  log-level [LEVEL]                   Get/set logging threshold for manager
  log-target [TARGET]                 Get/set logging target for manager
  service-watchdogs [BOOL]            Get/set service watchdog state

System Commands:
  is-system-running                   Check whether system is fully running
  default                             Enter system default mode
  rescue                              Enter system rescue mode
  emergency                           Enter system emergency mode
  halt                                Shut down and halt the system
  poweroff                            Shut down and power-off the system
  reboot                              Shut down and reboot the system
  kexec                               Shut down and reboot the system with kexec
  exit [EXIT_CODE]                    Request user instance or container exit
  switch-root ROOT [INIT]             Change to a different root file system
  suspend                             Suspend the system
  hibernate                           Hibernate the system
  hybrid-sleep                        Hibernate and suspend the system
  suspend-then-hibernate              Suspend the system, wake after a period of
                                      time, and hibernate

#350 Systemd 的问题

Linux Systemd 2019-12-20

开源中国上看到 Debian 正在投票是否支持非 systemd 初始化系统。

2014 年素来混乱的 Debian 社区，经过了一番激烈争论之后（甚至是生命安全威胁），终于决定支持 systemd。
PS: 这场争议导致部分核心人员离开，主要是对 Debian 社区的管理机制（混乱 “民主”）产生质疑。
2015 年 5 月发布的 Debian 8.0 (Jessie) 开始使用 Systemd 当默认的初始化系统。
但是关于 Systemd 的争论从未停止，甚至有部分开发者独自维护了一个拒绝 Systemd 的分叉：Devuan。

Systemd 真是闹出好大争议，和 GNOME3 一样。也正是有 GNOME3 的例子（社区总体来说，或者说大多数人，最后还是拥抱了变化，接纳 GNOME3），而且我只是一个实用主义的使用者，我觉得 Systemd 挺好的，能提升性能、使用又方便，为什么不呢。

#349 五险一金（武汉）以及个人所得税

武汉个人 2019-12-14

我不知道具体是怎么规定的，或者别的公司是怎么实施的，这里只是以我司（SendCloud）作为参考。
主要是我根据资料和自己的理解，结合实际数据，自己臆断的，不一定是真的，哈。

#348 读史书：兔死狗烹

阅读历史古文 2019-11-26

范蠡遂去，自齐遗大夫种书曰：“蜚鸟尽，良弓藏；狡兔死，走狗烹。越王为人长颈鸟喙，可与共患难，不可与共乐。子何不去？” 种见书，称病不朝。人或谗种且作乱，越王乃赐种剑曰：“子教寡人伐吴七术，寡人用其三而败吴，其四在子，子为我从先王试之。” 种遂自杀。
《史记越王勾践世家》

上令武士缚信，载后车。信曰：“果若人言，‘狡兔死，良狗亨；高鸟尽，良弓藏；敌国破，谋臣亡。’天下已定，我固当亨！” 上曰：“人告公反。” 遂械系信。至雒阳，赦信罪，以为淮阴侯。
《史记淮阴侯列传》

#347 MySQL 字段类型 `varchar` 和 `text` 的差异

DB MySQL 2019-11-25

一次数据库表结构调整，引起了我对 MySQL 字段类型 TEXT 和 VARCHAR 的思考。

#346 转载：2020年普及的乙醇汽油，价格会不会更便宜？

汽车乙醇汽油 2019-11-24

看到关于乙醇汽油使用推广的消息，就查了以下相关资料，这是看到的一篇老资讯了。

#345 容错、高可用、灾备

开发者架构阮一峰 2019-11-19

阮一峰的博文（容错，高可用和灾备）中说：

容错：发生故障时，如何让系统继续运行。
飞机的四个引擎坏了一个还能继续飞行，汽车的四个轮子坏了一个也能将就驾驶。
高可用：系统中断时，如何尽快恢复。
汽车的备胎，用于快速恢复正常驾驶（允许短暂的业务中断）。
灾备：系统毁灭时，如何抢救数据。
飞机的弹射装置，保证最核心的“资产” —— 驾驶员能够存活。

#344 开发者 Cheatsheets

开发者 2019-11-18

Linux

https://linuxopsys.com/topics/linux-commands-cheat-sheet
grep
awk

Bash & ShellScripting

https://oit.ua.edu/wp-content/uploads/2020/12/Linux_bash_cheat_sheet-1.pdf
http://www.cheat-sheets.org/saved-copy/shellscripcheatsheet.pdf

Linux Network

https://opensource.com/downloads/cheat-sheet-networking
- https://opensource.com/sites/default/files/gated-content/osdc_cheatsheet-networking-2021.4.8.pdf
Hacking Tools Cheat Sheet

Windows

cmd

http://www1.cs.columbia.edu/~sedwards/classes/2017/1102-spring/Command%20Prompt%20Cheatsheet.pdf
https://phoenixnap.com/kb/wp-content/uploads/2023/01/windows-cmd-commands-cheat-sheet-pdf.pdf

PowerShell

http://ramblingcookiemonster.github.io/images/Cheat-Sheets/powershell-basic-cheat-sheet2.pdf

Vim

https://phoenixnap.com/kb/vim-commands-cheat-sheet
https://www.cs.cmu.edu/~15131/f17/topics/vim/vim-cheatsheet.pdf
https://github.com/dennyzhang/cheatsheet-vim-A4
- https://github.com/dennyzhang/cheatsheet-vim-A4/blob/master/cheatsheet-vim-A4.pdf
https://gitee.com/chloneda/vim-cheatsheet

Python

https://hackr.io/blog/python-cheat-sheet
https://www.pythoncheatsheet.org/
https://static.realpython.com/python-cheat-sheet.pdf
https://static.realpython.com/python_cheat_sheet_v1.pdf
https://courses.cs.washington.edu/courses/cse163/22wi/resources/python-cheat-sheet.pdf

Django

http://cheat-sheets.org/saved-copy/django_reference_sheet.pdf
https://cheatography.com/ogr/cheat-sheets/django/
https://edu.anarcho-copy.org/Programming%20Languages/Python/Python%20CheatSheet/beginners_python_cheat_sheet_pcc_django.pdf
https://www.riptutorial.com/Download/django-rest-framework.pdf
https://books.agiliq.com/_/downloads/django-api-polls-tutorial/en/latest/pdf/

NumPy

http://www.cheat-sheets.org/saved-copy/numpy-cheat-sheet.20210604.pdf

Golang

http://www.cheat-sheets.org/saved-copy/go-lang-cheat-sheet-master.20181212/golang_refcard.pdf
https://golang.sk/images/blog/cheatsheets/go-cheat-sheet.pdf
https://github.com/fedir/go-tooling-cheat-sheet
- https://raw.githubusercontent.com/fedir/go-tooling-cheat-sheet/master/go-tooling-cheat-sheet.pdf

C/C++

http://dcjtech.info/wp-content/uploads/2017/09/C-Programming.pdf
https://cheatography.com/ashlyn-black/cheat-sheets/c-reference/
https://opensource.com/sites/default/files/gated-content/cheat_sheet_c.pdf
https://courses.cs.washington.edu/courses/cse351/14sp/sections/1/Cheatsheet-c.pdf
https://web.pa.msu.edu/people/duxbury/courses/phy480/Cpp_refcard.pdf
https://cheatography.com/technecure/cheat-sheets/c-cheatsheet/
https://cppcheatsheet.readthedocs.io/_/downloads/en/latest/pdf/
https://cheatography.com/benjy/cheat-sheets/c/

Java

https://computinglearner.com/wp-content/uploads/2021/09/Java-Cheat-Sheet.pdf

PHP

https://websitesetup.org/wp-content/uploads/2020/09/PHP-Cheat-Sheet.pdf

Web

HTML

https://html.com/wp-content/uploads/html-cheat-sheet.pdf

CSS

https://websitesetup.org/wp-content/uploads/2019/11/wsu-css-cheat-sheet-gdocs.pdf

JavaScript

https://websitesetup.org/wp-content/uploads/2020/09/Javascript-Cheat-Sheet.pdf

jQuery

https://websitesetup.org/wp-content/uploads/2017/01/wsu-jquery-cheat-sheet.pdf
https://cheat-sheets.org/saved-copy/wsu-jquery-cheat-sheet.pdf

Vue

https://learnvue.co/LearnVue-Vue-3-Cheatsheet.pdf
https://vuejs-tips.github.io/cheatsheet/vuejs-cheatsheet.pdf

Redis

http://stephendavies.org/cpsc350/redisCheatSheet.pdf

MySQL

https://phoenixnap.com/kb/wp-content/uploads/2021/04/MySQL-Commands-Cheat-Sheet-by-PhoenixNAP.pdf

MongoDB

https://cheatography.com/isaeus/cheat-sheets/mongodb/
http://stephendavies.org/cpsc350/mongoCheatSheet.pdf
https://www.goalkicker.com/MongoDBBook/MongoDBNotesForProfessionals.pdf

RabbitMQ

https://pika.readthedocs.io/_/downloads/en/stable/pdf/

工具

Git

https://education.github.com/git-cheat-sheet-education.pdf

Excel

https://download.microsoft.com/download/5/4/c/54cd97c1-0213-46a7-b659-95f1c9145f42/Excel_shortcuts_cheat_sheet.pdf

PyTorch

https://www.mad.tf.fau.de/files/2019/07/pytorch-cheatsheet-en.pdf

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