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Security

CentOS / Redhat: Turn On SELinux Protection

SELinux enforces the idea that programs should be limited in what files they can access and what actions they can take. However, by default it is turned off under RHEL / CentOS 5.x server? How do I turn it on? How can I enable SELinux on CentOS / RHEL 6 IBM server?
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Linux: Create /tmp And Mount as Partition File With the noexec, nosuid, And nodev

How do I mount /tmp as a separate filesystem (/root/images/tmpfile.bin) with the noexec,nosuid, nodev options under Linux like operating systems?
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Mac OS X Disable Unnecessary Services

How do I disable unnecessary services under Mac OS X to secure my Mac OS X based desktop / server / laptop?
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I‘ve brand new Ubuntu Linux server (Apache + PHP5 FastCGI + Lighttpd image only server) installed for my wordpress, mediawiki and vBullietin software. I can load forntpage of all software but user cannot edit any wiki pages or post anything and I get the following error in log file:

PHP Fatal error: Allowed Memory Size of 20971520 Bytes exhausted (tried to allocate 131072 bytes) in /usr/share/mediawiki/includes/OutputHandler.php on line 81

How do I fix this problem?
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CentOS / Redhat Apache mod_ssl Configuration

The mod_ssl module provides strong cryptography for the Apache Web server via the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols. How do I install and configure mod_ssl under CentOS / Fedora / Redhat Enterprise Linux?
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Mac OS X Display Access Warnings Message For The Login Window

I know how to display notice of a computer’s ownership, to warn against unauthorized access, under Linux gnome desktop. How do I display similar message under Apple Mac OS X to remind authorized users of their consent to monitoring?
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Linux Upgrade Password Hashing Algorithm to SHA-512

The default algorithm for storing password hashes in /etc/shadow is MD5. I was told to use SHA-512 hashing algorithm. How do I set password hashing using the SHA-256 and SHA-512 under CentOS or Redhat Enterprise Linux 5.4?
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Linux Kernel /etc/sysctl.conf Security Hardening

How do I set advanced security options of the TCP/IP stack and virtual memory to improve security and performance of my system? How do I configure Linux kernel to prevent certain kinds of attacks using /etc/sysctl.conf? How do I set Linux kernel parameters?
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Linux Iptables: Add / Delete An IP Address Remotely Using A Shell Script

I’ve root ssh access and need to add / delete a few IP address on fly using the IPtables command via local shell script. How do I add or delete an IP address remotely over the SSH session under CentOS / Redhat / RHEL / Debian / Ubuntu Linux?
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Samba: Linux Iptables Firewall Configuration

How do I configure iptables firewall under CentOS / Fedora / RHEL / Redhat Linux to allow access to the Samba server? How do I open TCP ports # 137, 138, 139 and 445 under Linux so that all Microsoft Windows machine can access files and printer on a Linux host?
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