摘要：我无法安装/更新 latexmk，因为它说本地 tex live（2019）比远程（2020）旧，但实际上我已经从官方安装了 texlive 2020来源。
注意： latexmk 文件存在于我的/Library/Tex/texbin/.
终端：
输入sudo tlmgr install latexmk，得到
sudo tlmgr install latexmk
sh: line 1: 35636 Abort trap: 6 wget --version > /dev/null 2>&1
tlmgr: Local TeX Live (2019) is older than remote repository (2020).
Cross release updates are only supported with
update-tlmgr-latest(.sh/.exe) --update
See https://tug.org/texlive/upgrade.html for details.
但是我的 latex 版本是 2020：输入latex --version，得到
pdfTeX 3.14159265-2.6-1.40.21 (TeX Live 2020)
kpathsea version 6.3.2
Copyright 2020 Han The Thanh (pdfTeX) et al.
There is NO warranty. Redistribution of this software is
covered by the terms of both the pdfTeX copyright and
the Lesser GNU General Public License.
For more information about these matters, see the file
named COPYING and the pdfTeX source.
Primary author of pdfTeX: Han The Thanh (pdfTeX) et al.
Compiled with libpng 1.6.37; using libpng 1.6.37
Compiled with zlib 1.2.11; using zlib 1.2.11
Compiled with xpdf version 4.02