How to copy all photos in gallery to linux desktop machine?
I assume you have Galaxy Tab with Honeycomb and don't have a SD card slot, but have 16/32 GBs of internal storage. In Honeycomb, MTP mode (Windows Media Transfer Protocol) is used instead of USB Mass storage. That's why it's isn't working for you perhaps.

First read what MTP is and why it's being used by OEMs now here. MTP and ICS. Also this Question should be useful - Android Stack Exchange - Can I disable MTP mode and just have a regular USB connection?

Have your tried enabling MTP support for Linux? These are the steps for a Ubuntu distro - Guide To Setup MTP.

Alternatively via using ADB I believe you can access Gallery files in /mnt/sdcard/. The sdcard folder should be there even if you don't have a SD card slot. Camera photos would be in /DCIM folder.

Full steps would be (if anyone needs) -

adb shell
cd /mnt/sdcard/DCIM/


You can check which folders exist here and verify if your Media files are here or not.