How to fix "no matching host key type found"
An SSH connection may fail with no matching host key type found when a newer client disables ssh-rsa and ssh-dss. These options configure compatibility.
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Security & access.
36 articles on this topic
Fixing SSH "no hostkey alg" on Debian/Ubuntu
If SSH to a Debian/Ubuntu server returns no hostkey alg, the SSH client failed the host key algorithm check while connecting. To fix it, check permissions…
How to fix an ssh connection refused with "no hostkey alg"
If connecting to a server over SSH fails with "no hostkey alg", as in the example below: debug1: Reading configuration data /etc/ssh_config debug1: Connecting to 192.168.1.1 [192.168.1.1] port 22.
How to change an iDRAC password using Racadm
Reset an iDRAC password directly from the server through OpenManage using racadm. Install OpenManage before following these steps.
Scanning heartbleed bug with the nmap NSE script
Heartbleed Bug: OpenSSL Security Flaw leaves secure-protocol services using OpenSSL 1.0.1 vulnerable. Administrators using OpenSSL need to check their systems.
Critical Security: Patch for OpenSSL Heartbleed Vulnerability
The OpenSSL Heartbleed bug (CVE-2014-0160) lets an attacker send a malformed heartbeat message and obtain data stored in the target machine's memory.
Heartbleed Bug: OpenSSL Security Flaw
Security researchers discovered Heartbleed (CVE-2014-0160), a bug in OpenSSL 1.0.1 through 1.0.1f and 1.0.2beta that can expose memory contents.
How to reset virus database on Zimbra
Zimbra uses ClamAV to scan email for viruses. Its virus database is normally updated regularly, but if updates fail, the database needs to be reset.
How to detect and prevent brute force attacks on Zimbra
Password policies in ZIMBRA can help prevent malicious users from guessing passwords through brute-force attacks, but this approach does not appear to resolve the problem completely.
How to set web server mode on Zimbra mail
To make webmail work over http, https, or both, change its operating mode using the steps below. Run the following command to change…
How to create self-signed certificate for Zimbra mail server
Zimbra Collaboration Suite (ZCS), or Zimbra mail server, uses certificates to secure its operation and communication. If a certificate expires, Zimbra cannot operate, so a new certificate is needed.
How to unlock Zimbra Accounts
Zimbra immediately locks an account after a configured number of failed login attempts to stop hackers repeatedly guessing passwords until they find the right one. If incorrect passwords reach the configured limit…
Configure SSH Keys authentication with PuTTY
PuTTY is a popular program for remotely accessing Linux. SSH key authentication makes logging in more convenient for system administrators.
Fix "zimbraRemoteManagementPrivateKeyPath (/opt/zimbra/.ssh/zimbra_identity) does not exist" on Zimbra Admin console
When using the Zimbra Admin console, clicking a menu to open its page may display an error window with this message: " server zimbra.mail.ezymailhosting.com zimbraRemoteManagementPrivateKey
How to create an admin account on Zimbra mail server
Creating an admin account and granting admin privileges to existing users on a Zimbra mail server. The command for creating an admin account is zmprov ca email password zimbraIsAdminAccount TRUE. An example follows.
Fix "Permission denied" issue when running zmsshkeygen command
If zmsshkeygen cannot generate a key because of a Permission denied error, as in this example: [zimbra@Ezymailhosting bin]$ ./zmsshkeygen Generating public/private dsa key pair. o
How to resolve "unable to determine enabled services from ldap"
After restarting the zimbra service or rebooting the server, you may encounter the following error when starting ldap: Starting ldap...Done. Unable to determine enabled services from ldap. Enabled services read f
Introducing Putty Manager
For PuTTY fans, I have a new tool to introduce. It is useful when you need several remote sessions and must run commands on multiple machines at once: Putty Manager. To use it, you need PuTTY…
Linux last Command – List Users Who Logged In
When you need to check login details, what comes to mind first? Many would look in /var/log/secure because it stores login history, but that can be cumbersome…
Openldap with Red Hat 6: ldapadd ldap_bind: Invalid credentials (49)
OpenLDAP in Red Hat Enterprise Linux 6 uses a new configuration layout. Users familiar with version 5 may see ldap_bind: Invalid credentials (49) when running ldapadd or ldapsearch.
Preventing thwart SSH attacks with DenyHosts
Soon after a server connects to the Internet, people begin trying to log in over SSH. If root login is allowed and the password is easy, the server may be compromised.
How to save/restore and backup iptables rules
Today I will cover a simple topic for anyone unfamiliar with the commands for saving, backing up, and restoring iptables rules. This article does not cover the iptables GUI. One problem with Linux iptables is that restarting…
How to install ClamAV on CentOS 5 (RHEL 5)
ClamAV is an open source antivirus widely used on Linux and Unix. This free antivirus integrates well with services and offers flexible configuration.
Free Antivirus 2011: Antivirus Software You Do Not Need to Buy from a Vendor
Antivirus 2011 Free: A list of free antivirus software for 2011 to download without buying from an antivirus vendor. Antivirus is essential for Windows computers…
[Resolved] Vulnerability in Firefox 3.5.1 Still bug with JavaScript
Firefox 3.5.1 fixed a JavaScript issue involving TraceMonkey. Subsequent reports of a security flaw were addressed by Mozilla, which said the issue did not affect security.
How to Disable Firewall on Red Hat Enterprise Linux, Centos
Red Hat Enterprise's firewall uses iptables, like other Linux distributions such as CentOS, Debian, SUSE, and Ubuntu. To enable or disable the firewall in Red Hat…
Enable Telnet in Linux Server
Linux does not enable Telnet because it is insecure, using SSH instead. To install and enable Telnet, install the telnet-server package.
Set passwords policy against a dictionary
Linux provides a module for password policy that prevents users from choosing easily guessed passwords. It is the pam_cracklib.so module in PAM.
Lock user after a set number of login attempts but also automatically unlock after 5 minutes
This article explains how to lock a user after a set number of login attempts using the pam_tally module in PAM.
Force users to change their passwords upon the first login
Linux can force users to change their passwords at their next login by locking the account, expiring the password, and unlocking the account.
Use IPv6 address be specified with scp, sftp and ssh
Use scp, sftp, and ssh with IPv6 addresses by enclosing the address in square brackets, as demonstrated with fe80::219:99ff:fe20:c251.
Configure the shell to logout automatically after a period of idle time.
On systems with many users, users who leave without logging out waste system resources. This method addresses that and also improves security…
Setup SSH to disable direct root login.
To prevent direct root login over SSH, edit #vi /etc/ssh/sshd_config and set PermitRootLogin to no: PermitRootLogin no. Then restart SSH.
Logout the user from ssh after 15 minutes of inactivity
For SSH security, configure the system to log out users after 15 minutes of inactivity by editing sshd_config.
Telnet as the root user
Telnet is usually disabled on Linux for security reasons. This article describes enabling direct root login through telnet.
When you forgot root password.
What can you do when you cannot log in because your password is rejected? After reading this article, you will be able to resolve the situation easily. I will cover two bootloaders…