There's a mistake on this page: http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_MRG/1.1/html/Realtim e_Tuning_Guide/sect-Realtime_Tuning_Guide-General_System_Tuning-gettimeo fday_speedup.html It talks about echo'ing values into /proc/sys/kernel/syscall64, whereas actually the file is /proc/sys/kernel/vsyscall64. The page should probably also document that echoing a value into this file results in an error, although it appears to have the desired effect.
Good catch, the path is wrong. On the other hand, echo'ing values is a valid operation: [root@void ~]# cat /proc/sys/kernel/vsyscall64 1 [root@void ~]# echo 0 > /proc/sys/kernel/vsyscall64 [root@void ~]# cat /proc/sys/kernel/vsyscall64 0 [root@void ~]# echo 1 > /proc/sys/kernel/vsyscall64 [root@void ~]# echo 0 > /proc/sys/kernel/vsyscall64 [root@void ~]# cat /proc/sys/kernel/vsyscall64 0 But we should add a not, such as the one we have on the ftrace section, remeinding the reader that "1 >" and "1>" have different meanings on the shell. So, yes, "echo 1> /proc/sys/kernel/vsyscall64" will fail.