![]() The Cyrus IMAP service, a popular mail delivery agent.Database security, with a focus on MySQL.He is joined on several chapters by administrator and developer Bill Lubanovic.A number of new security topics have been added for this edition, including: Bauer, a security consultant, network architect, and lead author of the popular Paranoid Penguin column in the Linux Journal, carefully outlines the security risks, defines precautions that can minimize those risks, and offers recipes for robust security. An all-inclusive resource for Linux users who wish to harden their systems, Linux Server Security covers general security such as intrusion detection and firewalling a hub, as well as key services such as DNS, the Apache Web server, mail, and secure shell.Author Michael D. The book focuses on the most common use of Linux-as a hub offering services to an organization or the Internet-and shows readers how to harden their hosts against attacks. Any server experiences casual probe attempts dozens of time a day, and serious break-in attempts with some frequency as well.This highly regarded book, originally titled Building Secure Servers with Linux, combines practical advice with a firm knowledge of the technical tools needed to ensure security. But security is the foremost concern of anyone providing such a service. Check out ssh's manual page ( man ssh) sometime to discover all of the different options available with this seemingly simple program.Linux consistently appears high up in the list of popular Internet servers, whether it's for the Web, anonymous FTP, or general services such as DNS and delivering mail. While it might mostly be used in its simplest form, ssh there are literally dozens of uses, with flags and configurations to make connections from one host to another. With this setting in ~/.ssh/config, any ssh connection to the remote host is accomplished by forwarding stdin and stdout through a secure connection from bastion-host. Prox圜ommand in ~/.ssh/configĪs with ProxyJump, Prox圜ommand can be set in the ~/.ssh/config file for hosts that always use this configuration: Host remote-host The %h:%p arguments to the -W flag above specify to forward standard in and out to the remote host ( %h) and the remote host’s port ( %p). The Prox圜ommand itself is a specific command used to connect to a remote server-in the case of the earlier example, that would be the manual ssh command used to first connect to the bastion: $ ssh -o Prox圜ommand="ssh -W %h:%p bastion-host" remote-host Prox圜ommand works by forwarding standard in (stdin) and standard out (stdout) from the remote machine through the proxy or bastion hosts. ProxyJump is the simplified way to use a feature that ssh has had for a long time: Prox圜ommand. An alternative: Forwarding stdin and stdout The ssh command first creates a connection to the bastion host bastion-hostname (the host referenced, by nickname, in the remote host’s ProxyJump settings) before connecting to the remote host. Using the example configuration above, when an ssh connection is made like so: $ ssh remote-host-nickname The -J flag provides flexibiltiy for easily specifying proxy and remote hosts as needed, but if a specific bastion host is regularly used to connect to a specific remote host, the ProxyJump configuration can be set in ~/.ssh/config to automatically make the connection to the bastion en-route to the remote host: # The Bastion Host For example, a public bastion host giving access to a "web tier" set of hosts, within which is a further protected "database tier" group might be accessed. This feature is useful if there are multiple levels of separation between a bastion and the final remote host. The ssh man (or manual) page ( man ssh) notes that multiple, comma-separated hostnames can be specified to jump through a series of hosts: $ ssh -J, You can also set specific usernames and ports if they differ between the hosts: $ ssh -J To use it, specify the bastion host to connect through after the -J flag, plus the remote host: $ ssh -J The ProxyJump, or the -J flag, was introduced in ssh version 7.3. Instead of first SSHing to the bastion host and then using ssh on the bastion to connect to the remote host, ssh can create the initial and second connections itself by using ProxyJump. The ssh command has an easy way to make use of bastion hosts to connect to a remote host with a single command. ![]() How well do you know Linux? Take a quiz and get a badge.Linux system administration skills assessment.A guide to installing applications on Linux.Download RHEL 9 at no charge through the Red Hat Developer program. ![]()
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