add the above parameters to /etc/sysconfig/cpuspeed or use the performance governor by adding the following parameter to the /etc/sysconfig/cpuspeed file and restart the cpuspeed service:
On RHEL 6:
configure the performance cpuspeed governor as above for RHEL 5 and add the following kernel boot options and restart the server. More information available in the Low Latency Performance Tuning for Red Hat Enterprise Linux 6 article.
By default, NetworkManager on Red Hat Enterprise Linux (RHEL) 8 dynamically updates the /etc/resolv.conf file with the DNS settings from active NetworkManager connection profiles. This section describes different options on how to disable this feature to manually configure DNS settings in /etc/resolv.conf.
31.1. Disabling DNS processing in the NetworkManager configuration
This section describes how to disable DNS processing in the NetworkManager configuration to manually configure the /etc/resolv.conf file.
As the root user, create the /etc/NetworkManager/conf.d/90-dns-none.conf file with the following content by using a text editor: [main] dns=none
Reload the NetworkManager service: # systemctl reload NetworkManagerNote After you reload the service, NetworkManager no longer updates the /etc/resolv.conf file. However, the last contents of the file are preserved.
Optionally, remove the Generated by NetworkManager comment from /etc/resolv.conf to avoid confusion.
Edit the /etc/resolv.conf file and manually update the configuration.
Reload the NetworkManager service: # systemctl reload NetworkManager
Display the /etc/resolv.conf file: # cat /etc/resolv.conf If you successfully disabled DNS processing, NetworkManager did not override the manually configured settings.
For further details, see the description of the dns parameter in the NetworkManager.conf(5) man page.
31.2. Replacing /etc/resolv.conf with a symbolic link to manually configure DNS settings
NetworkManager does not automatically update the DNS configuration if /etc/resolv.conf is a symbolic link. This section describes how to replace /etc/resolv.conf with a symbolic link to an alternative file with the DNS configuration.
The rc-manager option is not set to file. To verify, use the NetworkManager --print-config command.
Create a file, such as /etc/resolv.conf.manually-configured, and add the DNS configuration for your environment to it. Use the same parameters and syntax as in the original /etc/resolv.conf.
Remove the /etc/resolv.conf file: # rm /etc/resolv.conf
Create a symbolic link named /etc/resolv.conf that refers to /etc/resolv.conf.manually-configured: # ln -s /etc/resolv.conf.manually-configured /etc/resolv.conf
For details about parameters you can set in /etc/resolv.conf, see the resolv.conf(5) man page.
For further details about why NetworkManager does not process DNS settings if /etc/resolv.conf is a symbolic link, see the description of the rc-manager parameter in the NetworkManager.conf(5) man page.
You can login to a remote Linux server without entering password in 3 simple steps using ssky-keygen and ssh-copy-id as explained in this article.
ssh-keygen creates the public and private keys. ssh-copy-id copies the local-host’s public key to the remote-host’s authorized_keys file. ssh-copy-id also assigns proper permission to the remote-host’s home, ~/.ssh, and ~/.ssh/authorized_keys.
This article also explains 3 minor annoyances of using ssh-copy-id and how to use ssh-copy-id along with ssh-agent.
Sometime NFS can result in to weird problems. For example NFS mounted directories sometimes contain stale file handles. If you run command such as ls or vi you will see an error: $ ls .: Stale File Handle
First let us try to understand the concept of Stale File Handle. Managing NFS and NIS, 2nd Edition book defines filehandles as follows (a good book if you would like to master NFS and NIS): A filehandle becomes stale whenever the file or directory referenced by the handle is removed by another host, while your client still holds an active reference to the object. A typical example occurs when the current directory of a process, running on your client, is removed on the server (either by a process running on the server or on another client).
So this can occur if the directory is modified on the NFS server, but the directories modification time is not updated.
First command (umount) forcefully unmount a disk partition /mnt/local (NFS).
(b) Or try to mount NFS directory with the noac option. However I don’t recommend using noac option because of performance issue and Checking files on NFS filesystem referenced by file descriptors (i.e. the fcntl and ioctl families of functions) may lead to inconsistent result due to the lack of consistency check in kernel even if noac is used.
LVM 是逻辑盘卷管理（Logical Volume Manager）的简称，最早是 IBM 为 AIX 研发的存储管理机制。LVM 通过在硬盘和分区之间建立一个逻辑层，可以让多个分区或者物理硬盘作为一个逻辑卷 ( 相当于一个逻辑硬盘 )，提高了磁盘分区管理的灵活性。1998 年，Heinz Mauelshagen 在 Linux 2.4 内核上提供了 Linux 的 LVM 实现。目前 Linux 2.6 内核支持 LVM2，Redhat 官方网站目前提供最新可下载版本为 2.2.02.77；如果需要最新或者其它版本，请参考网页。
LVM 早期多用于服务器，配合存储硬件的 Raid 技术，提供高可靠性，可灵活配置的磁盘分区管理；普通 PC 由于存储容量有限，很少使用这种技术。随着单个磁盘容量的不断扩大和硬盘价格的下降，普通 PC 拥有 TB 级的大容量存储空间逐渐普及，也带来对 PC 上存储管理的需要，LVM 无疑是很好的解决方案。只是普通 PC 用户由于缺少硬件冗余保护，在发生灾难时，通常会发生比较严重的数据损失。好在 LVM 提供了一系列灾难恢复的功能，可以帮助普通 PC 用户尽可能减少损失。 我们可以通过下面的命令检查系统中是否安装了 lvm 工具：
This tutorial explains how to setup and use an SFTP server on
CentOS. Before I start, let me explain what actually SFTP represents and
what it is used for. Currently, most people know that we can use normal
FTP for transferring, downloading or uploading data from a server to
client or client to server. But this protocol is getting hacked easily
(if TLS is not used) by anonymous intruders as it the ports are wide
open to anyone. Therefore, SFTP has been introduced to as another
alternative to meet the main purpose to strengthen the security level.
SFTP stands for SSH File Transfer Protocol or Secure File
Transfer Protocol. It uses a separate protocol packaged with SSH to
provide a secure connection.
1. Preliminary Note
For this tutorial, I am using CentOS 7 in the 64bit version.
The same steps will work on CentOS 6 as well. The tutorial result will
show how a client can be provided with access to the SFTP server but
unable to login to the server itself by SSH.
2. SFTP Installation
Unlike normal FTP, there’s no need to install additional
packages in order to use SFTP. We just require the prebuild SSHd package
that got already installed during installation on the server.
Therefore, just check to confirm if you already have the required SSH
package. Below are the steps: