December 19, 2021

[Note] HEIC

Environment: Ubuntu 20


Photos from iPhone->Google Photo->Download saves as .HEIC, can't view on Linux.


$ sudo apt install heif-gdk-pixbuf

$ sudo apt install libheif-examples

$ heif-convert -q 90 [HEIC file] [filename.jpg]

December 12, 2021

[Note] Ubuntu VirtualBox + VirtualBox Extension Pack


Ubuntu 20.04, VirtualBox 6.1.30 r148432

VBox was updated multiple times.



sudo apt install fails to install VBox Extension Pack 


$ sudo apt install virtualbox-ext-pack

Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
0 upgraded, 1 newly installed, 0 to remove and 3 not upgraded.
Need to get 10.6 kB of archives.
After this operation, 142 kB of additional disk space will be used.
Get:1 focal-updates/multiverse amd64 virtualbox-ext-pack all 6.1.26-2~ubuntu1.20.04.1 [10.6 kB]


Progress state: NS_ERROR_FAILURE
VBoxManage: error: Failed to install "/usr/share/virtualbox-ext-pack/Oracle_VM_VirtualBox_Extension_Pack-6.1.26.vbox-extpack"
VBoxManage: error: VBoxExtPackRegister returned VERR_VERSION_MISMATCH, pReg=0000000000000000 ErrInfo='Helper version mismatch - expected 0x3 got 0x30000'
VBoxManage: error: Details: code NS_ERROR_FAILURE (0x80004005), component ExtPackManagerWrap, interface IExtPackManager
VBoxManage: error: Context: "RTEXITCODE handleExtPack(Ha
ndlerArg*)" at line 1424 of file VBoxManageMisc.cpp
Installation error: License key incorrect or unknown problem during installation.
dpkg: error processing package virtualbox-ext-pack (--configure):
 installed virtualbox-ext-pack package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
E: Sub-process /usr/bin/dpkg returned an error code (1)


  1. Make sure all VMs are closed.
  2. Open
  3. (firefox was used) Click on Oracle_VM_VirtualBox_Extension_Pack-6.1.30.vbox-extpack
  4. It'll ask to open with Oracle VM VirtualBox - click Ok.
  5. Check: open VBox Manager -> File -> Preferences -> Extensions

[Note] HWP 1.51 file conversion

Converting HWP 1.51 file to UTF8

1. Save as new (@V), select ASCII - KS

2. From Linux,  

$ iconv -f uhc -t utf8 KS2.TXT > /tmp/out.txt


  • hwp2txt v3 produces zero byte file
  • hwp2txt v1.2 converts to some unknown encoding (chardet couldn't detect)
  • enca can't detect
  • used chardet to detect the encoding uhc (EUC-KR).



send key events from Linux to DOSBox to automate saving in KS-ASCII encoding, or find correct hwp2txt version.


December 11, 2021

[Bookmark] SDR air traffic signal (video in Korean)

[NOTE] log4j security issue


Apache Log4j2 <=2.14.1 JNDI features used in configuration, log messages, and parameters do not protect against attacker controlled LDAP and other JNDI related endpoints. An attacker who can control log messages or log message parameters can execute arbitrary code loaded from LDAP servers when message lookup substitution is enabled. From log4j 2.15.0, this behavior has been disabled by default. In previous releases (>2.10) this behavior can be mitigated by setting system property "log4j2.formatMsgNoLookups" to “true” or by removing the JndiLookup class from the classpath (example: zip -q -d log4j-core-*.jar org/apache/logging/log4j/core/lookup/JndiLookup.class). Java 8u121 (see protects against remote code execution by defaulting "com.sun.jndi.rmi.object.trustURLCodebase" and "com.sun.jndi.cosnaming.object.trustURLCodebase" to "false".

Remedy - for now, see