sysctl command HowTo - Linux / Unix Q & A from nixCraft

How to prevent unprivileged users from viewing dmesg command output on Linux

last updated June 13, 2017 in CentOS, Debian / Ubuntu, Linux, RedHat and Friends, Security, Suse

I want to restrict both normal users and root user inside LXD container “hypervisor” from viewing and using dmesg command output. How do I prevent non-root (unprivileged) Linux users from viewing the Linux kernel’s log buffer?

How to reload sysctl.conf variables on Linux

last updated February 8, 2016 in BASH Shell, CentOS, Debian / Ubuntu, Linux, Troubleshooting

I am new Linux system user. How do I reload all sysctl variables without rebooting my server?

FreeBSD find CPU (processor) temperature command

last updated July 11, 2018 in FreeBSD, FreeBSD Jails (VPS), Hardware, UNIX

I am a new FreeBSD Unix user. How do I get the temperature of an Intel or AMD processor (CPU) in FreeBSD using command line option? Is there a command line option for determining CPU temperature on FreeBSD Unix operating system?

Linux: Log Suspicious Martian Packets / Un-routable Source Addresses

last updated July 11, 2018 in Linux, Networking, Security

I run a web-server, and I would like to log packets with un-routable source addresses on Linux operating system. How can I log spoofed packets on a Debian, Ubuntu, CentOS/RHEL or any Linux based server? How can I log a Martian packet (packet from Mars) on Linux operating systems?

Ubuntu Linux: Turn On Exec-Shield Buffer Overflow Protection

last updated June 4, 2013 in Security, Ubuntu Linux

I am trying to set exec-shield protection on Linux as described here but getting the following error on Ubuntu Linux server version 12.04 LTS:

sysctl -w kernel.exec-shield=1
error: “kernel.exec-shield” is an unknown key

How do I fix this problem and make sure exec-shield buffer overflow protection security feature turned on Ubuntu Linux?

Linux: Turn On TCP SYN Cookie Protection

last updated April 14, 2013 in Linux, Networking, Security

I am under DoS attack. My cloud based server hosting company asked me to enable TCP SYN cookie protection to save my domain from SYN Attack. How do I turn on TCP Syn cookie protection under Ubuntu or CentOS Linux based server?

FreeBSD Laptop: Find Out Battery Life Status Command

last updated March 13, 2013 in BASH Shell, FreeBSD

I know how to find out battery life status using Linux operating system. How do I monitor battery status on a laptop running FreeBSD version 9.x?