According to Redhat doc's /dev/shm is 1/2 the physical memory assigned to the server. So, from your 'df' output you should have 64Gb memory in use. /dev/shm is used to store 'Shared Memory' pages for applications running on the server, but it stores the pages in memory so its faster to access. So, no, I wouldn't delete files from here, you could use 'lsof' to check on file/page usage but deleting them seems a little extreme. If you can reboot, then this would safely clean /dev/shm.