Not able to change runtime settings in /proc and /sys

Issue

• Not able to change the IO scheduler, getting 'cannot overwrite existing file' error.

[root@rhel6-debug ~]# ll /sys/block/sda/queue/scheduler
-rw-r--r-- 1 root root 4096 May 29 06:40 /sys/block/sda/queue/scheduler
[root@rhel6-debug ~]# uptime
 06:41:19 up 12 days, 15:36,  1 user,  load average: 0.29, 0.41, 0.36
[root@rhel6-debug ~]# cat /sys/block/sda/queue/scheduler
noop anticipatory deadline [cfq]
[root@rhel6-debug ~]# echo 'deadline' > /sys/block/sda/queue/scheduler
-bash: /sys/block/sda/queue/scheduler: cannot overwrite existing file
[root@rhel6-debug ~]# cat /sys/block/sda/queue/scheduler
noop anticipatory deadline [cfq]

• Not able to drop caches, getting 'cannot overwrite existing file' error.

[root@centos6-debug ~]# echo 3 > /proc/sys/vm/drop_caches 
-bash: /proc/sys/vm/drop_caches: cannot overwrite existing file