sysctl vs writing directly to /proc/*

sysctl is a tool for reading and modifying various kernel attributes. It is available in many Unix-like operating systems, including not only Linux, but also OpenBSD and FreeBSD, for example. sysctl is typically available both as a shell command and as a system call.

In Linux, the sysctl mechanism is additionally exposed as part of the procfs virtual filesystem, under /proc/sys.

Note that the sysctl syscall is deprecated in Linux; it is recommended to use /proc/sys instead (either directly or via the sysctl shell command).

References:

• Manpage for the sysctl syscall in Linux
• Manpage for the sysctl shell command in Linux