Hi!

 upd
 
Checking core main apps...
 
[core] is synced.
[main] is synced.
[apps] is synced.
 
:: Synchronizing package databases...
 core is up to date
 main is up to date
 apps is up to date
:: Starting full system upgrade...
resolving dependencies...
looking for conflicting packages...

Package (21)         Old Version  New Version  Net Change  Download Size

main/dav1d           0.6.0-1      0.7.0-1        0.02 MiB       0.36 MiB
main/ffmpeg          4.2.2-6      4.2.3-1        0.00 MiB       9.30 MiB
main/freetds         1.1.39-1     1.1.40-1       0.00 MiB       0.66 MiB
main/gdb             9.1-3        9.2-1          0.00 MiB       3.41 MiB
main/geoip-database  20181009-1   20200524-1     0.12 MiB       1.47 MiB
core/glib2           2.64.2-1     2.64.3-1       0.02 MiB       2.75 MiB
main/imagemagick     6.9.11.13-1  6.9.11.14-1    0.00 MiB       2.37 MiB
main/iso-codes       4.4-1        4.5.0-1        0.17 MiB       3.16 MiB
core/krb5            1.18.1-1     1.18.2-1       0.00 MiB       1.31 MiB
main/lame            3.100-1      3.100-2       -0.04 MiB       0.31 MiB
main/libblockdev     2.23-1       2.24-1         0.12 MiB       0.25 MiB
main/libexif         0.6.21-5     0.6.22-1       0.49 MiB       0.50 MiB
main/libnice         0.1.16-3     0.1.17-1       0.02 MiB       0.27 MiB
apps/micro           2.0.3-1      2.0.4-1        0.03 MiB       4.16 MiB
main/mpv             0.32.0-2     0.32.0-3       0.00 MiB       1.31 MiB
main/python2-six     1.14.0-1     1.15.0-1       0.00 MiB       0.02 MiB
main/python3-cython  0.29.17-1    0.29.19-1     -0.15 MiB       1.94 MiB
main/python3-six     1.14.0-1     1.15.0-1       0.00 MiB       0.02 MiB
core/util-linux      2.35.1-2     2.35.2-1       0.02 MiB       2.98 MiB
main/v4l-utils       1.18.1-1     1.20.0-1       0.12 MiB       1.32 MiB
core/zstd            1.4.4-1      1.4.5-1       -0.07 MiB       2.72 MiB

Total Download Size:    40.60 MiB
Total Installed Size:  150.94 MiB
Net Upgrade Size:        0.89 MiB

:: Proceed with installation? [Y/n] y
:: Retrieving packages...
 glib2-2.64.3-1-x86_64                                                                            2.7 MiB   248 KiB/s 00:11 [--------------------------------------------------------------------------] 100%
 util-linux-2.35.2-1-x86_64                                                                       3.0 MiB   454 KiB/s 00:07 [--------------------------------------------------------------------------] 100%
 zstd-1.4.5-1-x86_64                                                                              2.7 MiB   668 KiB/s 00:04 [--------------------------------------------------------------------------] 100%
 krb5-1.18.2-1-x86_64                                                                          1338.5 KiB   746 KiB/s 00:02 [--------------------------------------------------------------------------] 100%
 dav1d-0.7.0-1-x86_64                                                                           371.4 KiB   345 KiB/s 00:01 [--------------------------------------------------------------------------] 100%
 lame-3.100-2-x86_64                                                                            321.7 KiB   386 KiB/s 00:01 [--------------------------------------------------------------------------] 100%
 v4l-utils-1.20.0-1-x86_64                                                                     1356.4 KiB   219 KiB/s 00:06 [--------------------------------------------------------------------------] 100%
 ffmpeg-4.2.3-1-x86_64                                                                            9.3 MiB   463 KiB/s 00:21 [--------------------------------------------------------------------------] 100%
 freetds-1.1.40-1-x86_64                                                                        674.2 KiB   525 KiB/s 00:01 [--------------------------------------------------------------------------] 100%
 gdb-9.2-1-x86_64                                                                                 3.4 MiB   560 KiB/s 00:06 [--------------------------------------------------------------------------] 100%
 geoip-database-20200524-1-x86_64                                                              1504.9 KiB   659 KiB/s 00:02 [--------------------------------------------------------------------------] 100%
 imagemagick-6.9.11.14-1-x86_64                                                                   2.4 MiB   765 KiB/s 00:03 [--------------------------------------------------------------------------] 100%
 iso-codes-4.5.0-1-x86_64                                                                         3.2 MiB   483 KiB/s 00:07 [--------------------------------------------------------------------------] 100%
 python3-six-1.15.0-1-x86_64                                                                     24.3 KiB  95.0 KiB/s 00:00 [--------------------------------------------------------------------------] 100%
 libblockdev-2.24-1-x86_64                                                                      255.7 KiB   248 KiB/s 00:01 [--------------------------------------------------------------------------] 100%
 libexif-0.6.22-1-x86_64                                                                        510.3 KiB   493 KiB/s 00:01 [--------------------------------------------------------------------------] 100%
 libnice-0.1.17-1-x86_64                                                                        278.2 KiB   210 KiB/s 00:01 [--------------------------------------------------------------------------] 100%
 mpv-0.32.0-3-x86_64                                                                           1342.8 KiB   191 KiB/s 00:07 [--------------------------------------------------------------------------] 100%
 python2-six-1.15.0-1-x86_64                                                                     22.8 KiB   345 KiB/s 00:00 [--------------------------------------------------------------------------] 100%
 python3-cython-0.29.19-1-x86_64                                                               1982.3 KiB   286 KiB/s 00:07 [--------------------------------------------------------------------------] 100%
 micro-2.0.4-1-x86_64                                                                             4.2 MiB   378 KiB/s 00:11 [--------------------------------------------------------------------------] 100%
(21/21) checking keys in keyring                                                                                            [--------------------------------------------------------------------------] 100%
(21/21) checking package integrity                                                                                          [--------------------------------------------------------------------------] 100%
:: File /var/cache/pacman/pkg/krb5-1.18.2-1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (checksum)).
Do you want to delete it? [Y/n] y
error: failed to commit transaction (invalid or corrupted package)
Errors occurred, no packages were upgraded

How to resolve this issue?

Looks like you have a corrupted local database, force syncing the database with sudo pacman -Syy, then update again (either upd or sudo pacman -Syu)

    demm Still the same result..

    ~sudo pacman -Syy
Password: 
:: Synchronizing package databases...
 core                                                                                            50.4 KiB  44.6 KiB/s 00:01 [--------------------------------------------------------------------------] 100%
 main                                                                                           187.9 KiB   136 KiB/s 00:01 [--------------------------------------------------------------------------] 100%
 apps                                                                                           186.4 KiB   896 KiB/s 00:00 [--------------------------------------------------------------------------] 100%
 
~  sudo pacman -Syu
:: Synchronizing package databases...
 core is up to date
 main is up to date
 apps is up to date
:: Starting full system upgrade...
resolving dependencies...
looking for conflicting packages...

Package (21)         Old Version  New Version  Net Change  Download Size

main/dav1d           0.6.0-1      0.7.0-1        0.02 MiB               
main/ffmpeg          4.2.2-6      4.2.3-1        0.00 MiB               
main/freetds         1.1.39-1     1.1.40-1       0.00 MiB               
main/gdb             9.1-3        9.2-1          0.00 MiB               
main/geoip-database  20181009-1   20200524-1     0.12 MiB               
core/glib2           2.64.2-1     2.64.3-1       0.02 MiB               
main/imagemagick     6.9.11.13-1  6.9.11.14-1    0.00 MiB               
main/iso-codes       4.4-1        4.5.0-1        0.17 MiB               
core/krb5            1.18.1-1     1.18.2-1       0.00 MiB       1.31 MiB
main/lame            3.100-1      3.100-2       -0.04 MiB               
main/libblockdev     2.23-1       2.24-1         0.12 MiB               
main/libexif         0.6.21-5     0.6.22-1       0.49 MiB               
main/libnice         0.1.16-3     0.1.17-1       0.02 MiB               
apps/micro           2.0.3-1      2.0.4-1        0.03 MiB               
main/mpv             0.32.0-2     0.32.0-3       0.00 MiB               
main/python2-six     1.14.0-1     1.15.0-1       0.00 MiB               
main/python3-cython  0.29.17-1    0.29.19-1     -0.15 MiB               
main/python3-six     1.14.0-1     1.15.0-1       0.00 MiB               
core/util-linux      2.35.1-2     2.35.2-1       0.02 MiB               
main/v4l-utils       1.18.1-1     1.20.0-1       0.12 MiB               
core/zstd            1.4.4-1      1.4.5-1       -0.07 MiB               

Total Download Size:     1.31 MiB
Total Installed Size:  150.94 MiB
Net Upgrade Size:        0.89 MiB

:: Proceed with installation? [Y/n] y
:: Retrieving packages...
 krb5-1.18.2-1-x86_64                                                                          1338.5 KiB   281 KiB/s 00:05 [--------------------------------------------------------------------------] 100%
(21/21) checking keys in keyring                                                                                            [--------------------------------------------------------------------------] 100%
(21/21) checking package integrity                                                                                          [--------------------------------------------------------------------------] 100%
:: File /var/cache/pacman/pkg/krb5-1.18.2-1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (checksum)).
Do you want to delete it? [Y/n] y
error: failed to commit transaction (invalid or corrupted package)
Errors occurred, no packages were upgraded.

      Which mirror do you use? Post /etc/pacman.d/mirrorlist. Try another mirror too (after setting a different mirror, use pacman -Syy again), by commenting out the current mirror and uncommenting another.

      @demm Your idea worked))

      I switched to the default Princeton mirror, which has been infuriatingly slow since Feb '20

      sudo pacman -Syy
Password: 
:: Synchronizing package databases...
error: failed retrieving file 'core.db' from mirror.math.princeton.edu : Connection timed out after 10000 milliseconds
 core                                                                                            50.4 KiB  61.5 KiB/s 00:01 [--------------------------------------------------------------------------] 100%
 main                                                                                           187.9 KiB  5.50 KiB/s 00:34 [--------------------------------------------------------------------------] 100%
 apps                                                                                           186.4 KiB  8.13 KiB/s 00:23 [--------------------------------------------------------------------------] 100%
  ~  sudo pacman -Syu
:: Synchronizing package databases...
 core is up to date
 main is up to date
 apps is up to date
:: Starting full system upgrade...
resolving dependencies...
looking for conflicting packages...

Package (21)         Old Version  New Version  Net Change  Download Size

main/dav1d           0.6.0-1      0.7.0-1        0.02 MiB               
main/ffmpeg          4.2.2-6      4.2.3-1        0.00 MiB               
main/freetds         1.1.39-1     1.1.40-1       0.00 MiB               
main/gdb             9.1-3        9.2-1          0.00 MiB               
main/geoip-database  20181009-1   20200524-1     0.12 MiB               
core/glib2           2.64.2-1     2.64.3-1       0.02 MiB               
main/imagemagick     6.9.11.13-1  6.9.11.14-1    0.00 MiB               
main/iso-codes       4.4-1        4.5.0-1        0.17 MiB               
core/krb5            1.18.1-1     1.18.2-1       0.00 MiB       1.31 MiB
main/lame            3.100-1      3.100-2       -0.04 MiB               
main/libblockdev     2.23-1       2.24-1         0.12 MiB               
main/libexif         0.6.21-5     0.6.22-1       0.49 MiB               
main/libnice         0.1.16-3     0.1.17-1       0.02 MiB               
apps/micro           2.0.3-1      2.0.4-1        0.03 MiB               
main/mpv             0.32.0-2     0.32.0-3       0.00 MiB               
main/python2-six     1.14.0-1     1.15.0-1       0.00 MiB               
main/python3-cython  0.29.17-1    0.29.19-1     -0.15 MiB               
main/python3-six     1.14.0-1     1.15.0-1       0.00 MiB               
core/util-linux      2.35.1-2     2.35.2-1       0.02 MiB               
main/v4l-utils       1.18.1-1     1.20.0-1       0.12 MiB               
core/zstd            1.4.4-1      1.4.5-1       -0.07 MiB               

Total Download Size:     1.31 MiB
Total Installed Size:  150.94 MiB
Net Upgrade Size:        0.89 MiB

:: Proceed with installation? [Y/n] y
:: Retrieving packages...
 krb5-1.18.2-1-x86_64                                                                          1338.5 KiB  5.68 KiB/s 03:56 [--------------------------------------------------------------------------] 100%
(21/21) checking keys in keyring                                                                                            [--------------------------------------------------------------------------] 100%
(21/21) checking package integrity                                                                                          [--------------------------------------------------------------------------] 100%
(21/21) loading package files                                                                                               [--------------------------------------------------------------------------] 100%
(21/21) checking for file conflicts                                                                                         [--------------------------------------------------------------------------] 100%
(21/21) checking available disk space                                                                                       [--------------------------------------------------------------------------] 100%
:: Processing package changes...
( 1/21) upgrading dav1d                                                                                                     [--------------------------------------------------------------------------] 100%
( 2/21) upgrading lame                                                                                                      [--------------------------------------------------------------------------] 100%
( 3/21) upgrading glib2                                                                                                     [--------------------------------------------------------------------------] 100%
( 4/21) upgrading util-linux                                                                                                [--------------------------------------------------------------------------] 100%
( 5/21) upgrading zstd                                                                                                      [--------------------------------------------------------------------------] 100%
( 6/21) upgrading v4l-utils                                                                                                 [--------------------------------------------------------------------------] 100%
( 7/21) upgrading ffmpeg                                                                                                    [--------------------------------------------------------------------------] 100%
( 8/21) upgrading freetds                                                                                                   [--------------------------------------------------------------------------] 100%
( 9/21) upgrading gdb                                                                                                       [--------------------------------------------------------------------------] 100%
(10/21) upgrading geoip-database                                                                                            [--------------------------------------------------------------------------] 100%
(11/21) upgrading krb5                                                                                                      [--------------------------------------------------------------------------] 100%
(12/21) upgrading imagemagick                                                                                               [--------------------------------------------------------------------------] 100%
(13/21) upgrading iso-codes                                                                                                 [--------------------------------------------------------------------------] 100%
(14/21) upgrading python3-six                                                                                               [--------------------------------------------------------------------------] 100%
(15/21) upgrading libblockdev                                                                                               [--------------------------------------------------------------------------] 100%
(16/21) upgrading libexif                                                                                                   [--------------------------------------------------------------------------] 100%
(17/21) upgrading libnice                                                                                                   [--------------------------------------------------------------------------] 100%
(18/21) upgrading micro                                                                                                     [--------------------------------------------------------------------------] 100%
(19/21) upgrading mpv                                                                                                       [--------------------------------------------------------------------------] 100%
(20/21) upgrading python2-six                                                                                               [--------------------------------------------------------------------------] 100%
(21/21) upgrading python3-cython                                                                                            [--------------------------------------------------------------------------] 100%
:: Running post-transaction hooks...
(1/4) Updating icon theme caches...
(2/4) Creating temporary files...
(3/4) Updating the info directory file...
(4/4) Updating the desktop file MIME type cache...

      Thanks!

      demm

      Which mirror do you use?

      Czechia
      I switched from the default mirror back in Feb '20

       ~ rankmirrors -n 11 /etc/pacman.d/mirrorlist 
# Server list generated by rankmirrors on 2020-05-30
#
# KaOS repository mirrorlist
#
# Default mirror, USA
# Czech Republic
# France
# USA
# Germany
# United States
# Vietnam

Server = http://193.86.184.157/kaos/$repo
Server = http://kaos.youm.org/$repo
Server = http://kaosx.tk/repo/$repo
Server = http://kiiwii.cf/kaos/$repo
Server = http://mirror.dacentec.com/kaosx/$repo
Server = http://mirror6.layerjet.com/kaos/$repo
Server = http://mirrors.redcorelinux.org/kaosx/$repo
Server = https://kaos-frankfurt.tk/repo/$repo
Server = https://mirror.alpix.eu/kaos/$repo
Server = https://mirror.freedif.org/KaOS/$repo
Server = https://mirror.math.princeton.edu/pub/kaoslinux/$repo

        Try setting:

        Server = http://mirrors.redcorelinux.org/kaosx/$repo

        as first mirror, should be fast and closer to you (if the Czech was the fastest).
        I'll need to check why the Czech mirror is not syncing correctly, will email the owner.