出处：
https://docs.oracle.com/en-us/iaas/Content/FreeTier/freetier_topic-Always_Free_Resources.htm
Reclamation of Idle Compute Instances

Idle Always Free compute instances may be reclaimed by Oracle. Oracle will deem virtual machine and bare metal compute instances as idle if, during a 7-day period, the following are true:

CPU utilization for the 95th percentile is less than 10%
Network utilization is less than 10%
Memory utilization is less than 10% (applies to A1 shapes only)

比起切割图像，pdf 更好操作，比如 A3 打印成 A4, 只要在原始页面创建 4 个引用，分别定义 4 个打印区域（ CropBox ）就可以了，新的文档大小并不会有太大变化，类似的 python 项目
https://pdfposter.readthedocs.io/en/stable/Examples.html

vim 也提供了 arguments
-n No swap file will be used.

把 swap 关了就快了
～/.vimrc
set noswapfile

如果想更智能一点，
https://vi.stackexchange.com/questions/3484/disable-swap-file-for-large-files
https://www.vim.org/scripts/script.php?script_id=1506

遇到了哈希冲突，
ext4 uses half_md4 as a default hashing-mechanism. If I interpret my google-results correctly, this uses the md4-hash algorithm, but strips it to 32 bits.

https://blog.merovius.de/2013/10/20/ext4-mysterious-no-space-left-on.html

good question.
网页是从 doc/find.texi 生成的 （ Texinfo is the official documentation format of the GNU project ）
http://www.gnu.org/software/texinfo/manual/texinfo/texinfo.html#Adding-Output-Formats
> From time to time, proposals are made to generate traditional Unix man pages from Texinfo source. However, because man pages have a strict conventional format, creating a good man page requires a completely different source from that needed for the typical Texinfo applications of writing a good user tutorial and/or a good reference manual. This makes generating man pages incompatible with the Texinfo design goal of not having to document the same information in different ways for different output formats. You might as well write the man page directly.

find 的 man 应该是 https://git.savannah.gnu.org/cgit/findutils.git/plain/find/find.1 , 里面还是过时的信息，:(

查了下最新的 4.8.0, 文档已经修正了
https://git.savannah.gnu.org/cgit/findutils.git/plain/doc/find.texi
http://www.gnu.org/software/findutils/manual/html%5Fmono/find.html#Full-Name-Patterns

恭喜你找到了一个文档的 bug，文档和行为不匹配

IPV6 竟然查询失败，需要 curl -4 强制 IPV4
```
curl -c cookie.txt http://znts.189.cn/xyface/xyspeedDev/isTs.jhtml
{"code":101,"ip":"240e:388:8532:8300:d49b:1232:29c3:f40b","state":0,"message":"宽带不在线 [查询失败，用户不在线]"}%
```

ffmpeg -i a.mp4 -i b.mp4 -filter_complex hstack output.mp4

服务端处理+新版 FFMPEG hstack
https://ffmpeg.org/ffmpeg-filters.html#hstack
Stack input videos horizontally.
All streams must be of same pixel format and of same height.
Note that this filter is faster than using overlay and pad filter to create same output.

```
ffmpeg -i a.mp4 -i b.mp4 -filter_complex vstack output.mp4
```