用Arch Linux就是每天睡觉关机前滚一下，然而有时候有些软件升级滚出问题，比如glibc-2.28就导致了R安装包有问题，会抛出下面的错误：

terminate called after throwing an instance of 'std::runtime_error'
  what():  Mutex creation failed

用blogdown编译博客也同样会抛出这个错误。

然后electron也有问题，《开源的macOS和linux版微信》跑着跑着突然CPU就狂飙。

解决办法就是安装回老版本，但pacman永远是最新的，当然可以去git/svn仓库里找老版本的PKGBUILD，然后再makepkg，但经常会在signature checking这步报错，你还得到导入keyring，挺麻烦。

这时候我找到了downgrade脚本:

Bash script for downgrading one or more packages to a version in your cache or the A.L.A.

AUR有收录，安装非常简单：

~/github/PAM   master  yay -S downgrade 
[sudo] password for ygc: 
resolving dependencies...
looking for conflicting packages...

Packages (1) downgrade-6.0.0-2

Total Download Size:   0.01 MiB
Total Installed Size:  0.12 MiB

:: Proceed with installation? [Y/n] 
:: Retrieving packages...
 downgrade-6.0.0-2-any      9.0 KiB   242K/s 00:00 [###########] 100%
(1/1) checking keys in keyring                     [###########] 100%
(1/1) checking package integrity                   [###########] 100%
(1/1) loading package files                        [###########] 100%
(1/1) checking for file conflicts                  [###########] 100%
(1/1) checking available disk space                [###########] 100%
:: Processing package changes...
(1/1) installing downgrade                         [###########] 100%
Optional dependencies for downgrade
    sudo: for installation via sudo [installed]
:: Running post-transaction hooks...
(1/1) Arming ConditionNeedsUpdate...

这时候，我就可以用它来降低glibc的版本了，运行会列出各种版本：

 ~/github/PAM   master  downgrade glibc
Available packages:

*  1) glibc-2.28-1-x86_64.pkg.tar.xz (remote)
*  2) glibc-2.28-1-x86_64.pkg.tar.xz (local)
   3) glibc-2.27-3-x86_64.pkg.tar.xz (remote)
   4) glibc-2.27-2-x86_64.pkg.tar.xz (remote)
   5) glibc-2.26-11-x86_64.pkg.tar.xz (remote)
   6) glibc-2.26-10-x86_64.pkg.tar.xz (remote)
   7) glibc-2.26-9-x86_64.pkg.tar.xz (remote)
   8) glibc-2.26-8-x86_64.pkg.tar.xz (remote)
   9) glibc-2.26-7-x86_64.pkg.tar.xz (remote)
  10) glibc-2.26-6-x86_64.pkg.tar.xz (remote)
  11) glibc-2.26-5-x86_64.pkg.tar.xz (remote)
  12) glibc-2.26-4-x86_64.pkg.tar.xz (remote)
  13) glibc-2.26-3-x86_64.pkg.tar.xz (remote)
  14) glibc-2.26-2-x86_64.pkg.tar.xz (remote)
  15) glibc-2.26-1-x86_64.pkg.tar.xz (remote)
  16) glibc-2.25-7-x86_64.pkg.tar.xz (remote)
  17) glibc-2.25-6-x86_64.pkg.tar.xz (remote)
  18) glibc-2.25-5-x86_64.pkg.tar.xz (remote)
  19) glibc-2.25-4-x86_64.pkg.tar.xz (remote)
  20) glibc-2.25-3-x86_64.pkg.tar.xz (remote)
  21) glibc-2.25-2-x86_64.pkg.tar.xz (remote)
  22) glibc-2.25-1-x86_64.pkg.tar.xz (remote)
  23) glibc-2.24-2-x86_64.pkg.tar.xz (remote)
  24) glibc-2.24-1-x86_64.pkg.tar.xz (remote)
  25) glibc-2.23-5-x86_64.pkg.tar.xz (remote)
  26) glibc-2.23-4-x86_64.pkg.tar.xz (remote)
  27) glibc-2.23-3-x86_64.pkg.tar.xz (remote)
  28) glibc-2.23-2-x86_64.pkg.tar.xz (remote)
  29) glibc-2.23-1-x86_64.pkg.tar.xz (remote)
  30) glibc-2.22-4-x86_64.pkg.tar.xz (remote)

只需要选择其中某一个，就会自动下载安装：

select a package by number: 3
 glibc-2.27-3-x86_64                                          9.1 MiB  4.68M/s 00:02 [#################################################] 100%
 glibc-2.27-3-x86_64.sig                                    310.0   B  0.00B/s 00:00 [#################################################] 100%
loading packages...
warning: downgrading package glibc (2.28-1 => 2.27-3)
resolving dependencies...
looking for conflicting packages...

Packages (1) glibc-2.27-3

Total Installed Size:  41.40 MiB
Net Upgrade Size:      -4.15 MiB

:: Proceed with installation? [Y/n] 
(1/1) checking keys in keyring                                                       [#################################################] 100%
(1/1) checking package integrity                                                     [#################################################] 100%
(1/1) loading package files                                                          [#################################################] 100%
(1/1) checking for file conflicts                                                    [#################################################] 100%
(1/1) checking available disk space                                                  [#################################################] 100%
:: Processing package changes...
(1/1) downgrading glibc                                                              [#################################################] 100%
warning: /etc/locale.gen installed as /etc/locale.gen.pacnew
Generating locales...
  en_US.UTF-8... done
  zh_CN.UTF-8... done
Generation complete.
:: Running post-transaction hooks...
(1/4) Reloading system manager configuration...
(2/4) Creating temporary files...
(3/4) Arming ConditionNeedsUpdate...
(4/4) Updating the info directory file...
add glibc to IgnorePkg? [y/n] n
 ~/github/PAM   master 

于是升级带来的各自烦人的bug，就没有了。

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