LFCS Certification Kernel Parameter Modification 3

Question 1

What happens if the same sysctl parameter is defined in both /etc/sysctl.conf and a file in /etc/sysctl.d/?

Accepted Answer

The file in /etc/sysctl.d/ takes precedence due to alphabetical load order

Answer

Files in /etc/sysctl.d/ are processed after /etc/sysctl.conf in alphabetical order, so later files override earlier ones.

Question 2

Which command reads and displays a single kernel parameter value without changing it?

Accepted Answer

sysctl kernel.pid_max

Answer

Running 'sysctl <key>' without -w reads and prints the current value of that kernel parameter.

Question 3

A server is experiencing network issues. An admin suspects 'net.core.rmem_max' is too low. Which command shows its current value?

Accepted Answer

sysctl net.core.rmem_max

Answer

sysctl reads live kernel parameters directly from /proc/sys, giving the current effective value.

Question 4

What is the purpose of the kernel parameter 'net.ipv4.tcp_syncookies'?

Accepted Answer

Protects against SYN flood attacks by enabling SYN cookies

Answer

tcp_syncookies enables SYN cookies as a defense against SYN flood denial-of-service attacks.

Question 5

Which proc path would you write to in order to immediately disable IPv6 on interface eth0?

Accepted Answer

/proc/sys/net/ipv6/conf/eth0/disable_ipv6

Answer

Writing 1 to /proc/sys/net/ipv6/conf/eth0/disable_ipv6 immediately disables IPv6 on that interface.

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