I'm getting disk monitor alerts on /boot. How can I determine which files are safe to remove? 

-rw-r--r-- 1 root root 1271765 Jan 18 12:05 abi-3.19.0-47-generic 
-rw-r--r-- 1 root root 177779 Jul 24 18:19 config-3.19.0-25-generic 
-rw-r--r-- 1 root root 177790 Dec 2 05:19 config-3.19.0-39-generic 
-rw-r--r-- 1 root root 177808 Dec 8 13:32 config-3.19.0-41-generic 
-rw-r--r-- 1 root root 177808 Dec 18 06:36 config-3.19.0-42-generic 
-rw-r--r-- 1 root root 177808 Dec 31 11:40 config-3.19.0-43-generic 
-rw-r--r-- 1 root root 177808 Jan 18 12:05 config-3.19.0-47-generic 
drwxr-xr-x 5 root root 1024 Jan 20 06:48 grub 
-rw-r--r-- 1 root root 20752348 Dec 7 11:43 initrd.img-3.19.0-25-generic 
-rw-r--r-- 1 root root 20759486 Dec 8 06:44 initrd.img-3.19.0-39-generic 
-rw-r--r-- 1 root root 20759188 Dec 17 07:01 initrd.img-3.19.0-41-generic 
-rw-r--r-- 1 root root 20758251 Dec 19 06:35 initrd.img-3.19.0-42-generic 
-rw-r--r-- 1 root root 20761822 Jan 6 06:53 initrd.img-3.19.0-43-generic 
-rw-r--r-- 1 root root 20761010 Jan 20 06:48 initrd.img-3.19.0-47-generic 
drwx------ 2 root root 12288 Dec 7 11:36 lost+found 
-rw-r--r-- 1 root root 176500 Mar 12 2014 memtest86+.bin 
-rw-r--r-- 1 root root 178176 Mar 12 2014 memtest86+.elf 
-rw-r--r-- 1 root root 178680 Mar 12 2014 memtest86+_multiboot.bin 
-rw------- 1 root root 3623533 Jul 24 18:19 System.map-3.19.0-25-generic 
-rw------- 1 root root 3628776 Dec 2 05:19 System.map-3.19.0-39-generic 
-rw------- 1 root root 3628871 Dec 8 13:32 System.map-3.19.0-41-generic 
-rw------- 1 root root 3628871 Dec 18 06:36 System.map-3.19.0-42-generic 
-rw------- 1 root root 3628871 Dec 31 11:40 System.map-3.19.0-43-generic 
-rw------- 1 root root 3628871 Jan 18 12:05 System.map-3.19.0-47-generic 
-rw------- 1 root root 6565968 Jul 24 18:19 vmlinuz-3.19.0-25-generic 
-rw------- 1 root root 6571728 Dec 2 05:19 vmlinuz-3.19.0-39-generic 
-rw------- 1 root root 6571728 Dec 8 13:32 vmlinuz-3.19.0-41-generic 
-rw------- 1 root root 6571600 Dec 18 06:36 vmlinuz-3.19.0-42-generic 
-rw------- 1 root root 6571600 Dec 31 11:40 vmlinuz-3.19.0-43-generic 
-rw------- 1 root root 6571600 Jan 18 12:05 vmlinuz-3.19.0-47-generic 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.mn-linux.org/pipermail/tclug-list/attachments/20160120/0b6fcf6e/attachment.html>