I just wanted to share with you guys the solution to this warning in the title I was getting lately in terminal window whenever I was using the Update Manager in Linux Mint 18.2 and 18.3. I've read in a post in the Arch Linux community forum that the warning is just that, a warning, that some size fields are missing in a theme's "index.theme" file, so nothing really to worry about. Also, I've read that the file which triggers the warning is in /usr/share/icons/[the name of the theme] directory, not in the /usr/share/themes directory So, I've opened the "/usr/share/icons/oxygen/index.theme" and in the "Directories" section there were some directories missing (i.e. not specified), while they existed as folders in the theme directory and, also, there were some directories mentioned (specifically the "intl" directories) in all Size fields, but they were not to be found as directories in the theme folder itself... Anyway, I made corrections in the "index.theme" file so that the "Directories" section had the missing directory specified and non-existing directories removed from the Directories section. Of course, the warning is now gone! So, here's the corrected code for the /usr/share/icons/oxygen/index.theme Code: [Icon Theme] Name=Oxygen Name[ast]=Oxygen Name[ca]=Oxygen Name[ca@valencia]=Oxygen Name[da]=Oxygen Name[de]=Oxygen Name[en_GB]=Oxygen Name[es]=Oxígeno Name[fi]=Oxygen Name[gl]=Oxygen Name[ko]=Oxygen Name[nl]=Oxygen Name[nn]=Oxygen Name[pl]=Tlen Name[pt]=Oxygen Name[pt_BR]=Oxygen Name[sk]=Oxygen Name[sl]=Kisik Name[sr]=Кисеоник Name[sr@ijekavian]=Кисеоник Name[sr@ijekavianlatin]=Kiseonik Name[sr@latin]=Kiseonik Name[sv]=Oxygen Name[uk]=Oxygen Name[x-test]=xxOxygenxx Name[zh_CN]=Oxygen Comment=Oxygen Team Comment[ca]=Equip de l'Oxygen Comment[ca@valencia]=Equip de l'Oxygen Comment[da]=Oxygen-holdet Comment[de]=Oxygen-Team Comment[en_GB]=Oxygen Team Comment[es]=El equipo de Oxígeno Comment[fi]=Oxygenin kehitysryhmä Comment[gl]=Equipo de Oxygen Comment[ko]=Oxygen 팀 Comment[nl]=Oxygen-team Comment[nn]=Oxygen-laget Comment[pl]=Zespół Oxygen Comment[pt]=Equipa do Oxygen Comment[pt_BR]=Equipe do Oxygen Comment[sk]=Tím Oxygen Comment[sl]=Ekipa Kisika Comment[sr]=Тим Кисеоника Comment[sr@ijekavian]=Тим Кисеоника Comment[sr@ijekavianlatin]=Tim Kiseonika Comment[sr@latin]=Tim Kiseonika Comment[sv]=Oxygen-gruppen Comment[uk]=Команда Oxygen Comment[x-test]=xxOxygen Teamxx Comment[zh_CN]=Oxygen 团队 DisplayDepth=32 Inherits=hicolor Example=folder LinkOverlay=link LockOverlay=lockoverlay ShareOverlay=share ZipOverlay=zip DesktopDefault=48 DesktopSizes=16,22,32,48,64,128,256 ToolbarDefault=22 ToolbarSizes=16,22,32,48 MainToolbarDefault=22 MainToolbarSizes=16,22,32,48 SmallDefault=16 SmallSizes=16,22,32,48 PanelDefault=32 PanelSizes=16,22,32,48,64,128,256 DialogDefault=32 DialogSizes=16,22,32,48,64,128,256 Directories=8x8/emblems,8x8/places,16x16/actions,16x16/animations,16x16/apps,16x16/categories,16x16/devices,16x16/emblems,16x16/emotes,16x16/mimetypes,16x16/places,16x16/special,16x16/status,22x22/actions,22x22/animations,22x22/apps,22x22/categories,22x22/devices,22x22/emblems,22x22/emotes,22x22/mimetypes,22x22/places,22x22/special,22x22/status,32x32/actions,32x32/animations,32x32/apps,32x32/categories,32x32/devices,32x32/emblems,32x32/emotes,32x32/mimetypes,32x32/places,32x32/status,48x48/actions,48x48/animations,48x48/apps,48x48/categories,48x48/devices,48x48/emblems,48x48/emotes,48x48/mimetypes,48x48/places,48x48/status,64x64/actions,64x64/apps,64x64/categories,64x64/devices,64x64/emblems,64x64/emotes,64x64/mimetypes,64x64/places,64x64/status,128x128/actions,128x128/apps,128x128/categories,128x128/devices,128x128/emblems,128x128/emotes,128x128/mimetypes,128x128/places,128x128/status,256x256/actions,256x256/applets,256x256/apps,256x256/categories,256x256/devices,256x256/mimetypes,256x256/places,256x256/status [8x8/emblems] Size=8 Context=Emblems Type=Threshold [8x8/places] Size=8 Context=Places Type=Threshold [16x16/actions] Size=16 Context=Actions Type=Threshold [16x16/animations] Size=16 Context=Animations Type=Threshold [16x16/apps] Size=16 Context=Applications Type=Threshold [16x16/categories] Size=16 Context=Categories Type=Threshold [16x16/devices] Size=16 Context=Devices Type=Threshold [16x16/emblems] Size=16 Context=Emblems Type=Threshold [16x16/emotes] Size=16 Context=Emotes Type=Threshold [16x16/mimetypes] Size=16 Context=MimeTypes Type=Threshold [16x16/places] Size=16 Context=Places Type=Threshold [16x16/special] Size=16 Context=Actions Type=Threshold [16x16/status] Size=16 Context=Status Type=Threshold [22x22/actions] Size=22 Context=Actions Type=Threshold [22x22/animations] Size=22 Context=Animations Type=Threshold [22x22/apps] Size=22 Context=Applications Type=Threshold [22x22/categories] Size=22 Context=Categories Type=Threshold [22x22/devices] Size=22 Context=Devices Type=Threshold [22x22/emblems] Size=22 Context=Emblems Type=Threshold [22x22/emotes] Size=22 Context=Emotes Type=Threshold [22x22/mimetypes] Size=22 Context=MimeTypes Type=Threshold [22x22/places] Size=22 Context=Places Type=Threshold [22x22/special] Size=22 Context=Actions Type=Threshold [22x22/status] Size=22 Context=Status Type=Threshold [32x32/actions] Size=32 Context=Actions Type=Threshold [32x32/animations] Size=32 Context=Animations Type=Threshold [32x32/apps] Size=32 Context=Applications Type=Threshold [32x32/categories] Size=32 Context=Categories Type=Threshold [32x32/devices] Size=32 Context=Devices Type=Threshold [32x32/emblems] Size=32 Context=Emblems Type=Threshold [32x32/emotes] Size=32 Context=Emotes Type=Threshold [32x32/mimetypes] Size=32 Context=MimeTypes Type=Threshold [32x32/places] Size=32 Context=Places Type=Threshold [32x32/status] Size=32 Context=Status Type=Threshold [48x48/actions] Size=48 Context=Actions Type=Threshold [48x48/animations] Size=48 Context=Animations Type=Threshold [48x48/apps] Size=48 Context=Applications Type=Threshold [48x48/categories] Size=48 Context=Categories Type=Threshold [48x48/devices] Size=48 Context=Devices Type=Threshold [48x48/emblems] Size=48 Context=Emblems Type=Threshold [48x48/emotes] Size=48 Context=Emotes Type=Threshold [48x48/mimetypes] Size=48 Context=MimeTypes Type=Threshold [48x48/places] Size=48 Context=Places Type=Threshold [48x48/status] Size=48 Context=Status Type=Threshold [64x64/actions] Size=64 Context=Actions Type=Threshold [64x64/apps] Size=64 Context=Applications Type=Threshold [64x64/categories] Size=64 Context=Categories Type=Threshold [64x64/devices] Size=64 Context=Devices Type=Threshold [64x64/emblems] Size=64 Context=Emblems Type=Threshold [64x64/emotes] Size=64 Context=Emotes Type=Threshold [64x64/mimetypes] Size=64 Context=MimeTypes Type=Threshold [64x64/places] Size=64 Context=Places Type=Threshold [64x64/status] Size=64 Context=Status Type=Threshold [128x128/actions] Size=128 Context=Actions Type=Threshold [128x128/apps] Size=128 Context=Applications Type=Threshold [128x128/categories] Size=128 Context=Categories Type=Threshold [128x128/devices] Size=128 Context=Devices Type=Threshold [128x128/emblems] Size=128 Context=Emblems Type=Threshold [128x128/emotes] Size=128 Context=Emotes Type=Threshold [128x128/mimetypes] Size=128 Context=MimeTypes Type=Threshold [128x128/places] Size=128 Context=Places Type=Threshold [128x128/status] Size=128 Context=Status Type=Threshold [256x256/actions] Size=256 Context=Actions Type=Threshold [256x256/applets] Size=256 Context=Applications Type=Scalable MinSize=48 MaxSize=256 [256x256/apps] Size=128 Context=Applications Type=Threshold [256x256/categories] Size=256 Context=Categories Type=Threshold [256x256/devices] Size=256 Context=Devices Type=Threshold [256x256/mimetypes] Size=256 Context=MimeTypes Type=Threshold [256x256/places] Size=256 Context=Places Type=Threshold [256x256/status] Size=256 Context=Status Type=Threshold