分类目录归档:系统管理

Windows\Linux\*nix系统管理

Linux 文件恢复的原理

inode 和 block

首先简单介绍一下 Linux 文件系统的最基本单元:inode。inode 译成中文就是索引节点,每个存储设备(例如硬盘)或存储设备的分区被格式化为文件系统后,应该有两部份,一部份是 inode,另一部份是 block,block 是用来存储数据用的。而 inode 呢,就是用来存储这些数据的信息,这些信息包括文件大小、属主、归属的用户组、读写权限等。inode 为每个文件进行信息索引,所以就有了 inode 的数值。linux 操作系统下可以使用 ls –id 命令来查看文件或者目录的 inode 值,一般”root”目录的 inode 值为 2,一个分区挂载到一个目录下时,这个”root”目录的 inode 值为 2

# mount /dev/sdb2 /tmp
# ls -id /tmp2 /tmp

文件恢复的原理

本文要介绍的命令是通过文件系统的 inode 值(一般是 2 )来获取文件系统信息。在 ext3 和 ext4 文件系统中,每个文件都是通过 inode 来描述其数据存放的具体位置,当文件被删除以后,inode 的数据指针部分被清零,文件目录区没有太多变化。文件的读写都是通过 inode 来实现,当 inode 数据指针被清零以后,即便文件内容还在,也没有办法把文件内容组合出来。当 ext3 和 ext4 文件系统中的元数据 metadata 发生变化时,相应的元数据 metadata 在日志文件会有一份拷贝。比如一个文件被删除了,它的 inode 信息会在日志文件中先保存一份,然后把要删除文件 inode 相关信息清零。这个日志文件是循环使用的,当操作过多时,删除的文件的 inode 日志记录会被新的数据替换,这就彻底丧失了根据 inode 找回数据的机会了。如果是大量文件的删除,这个日志文件会被反复循环利用多次,只留给最后删除的那些文件的恢复机会。

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Postfix+Amavisd-new+SpamAssassin+Clamav

一、安装Amavisd-new+SpamAssassin

说明:amavisd-new是介于MTA与邮件分析软件(如sa、clama)之间的一个接口;可以将位于队列的邮件取出来,调用ClamAV对邮件进行病毒扫描,调用SpamAssassin对邮件内容进行过滤 。

官方网站:

http://www.ijs.si/software/amavisd/

安装参考:

http://www.shisaa.jp/postset/mailserver-3.html

http://www.postfixvirtual.net/postfixantivirus.html#amavisdnew

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Log Parser Rocks! More than 50 Examples!

Log Parser is a tool that has been around for quite some time (almost six years, in fact).  I can’t really do any better than the description on the official download page, so here it is: “Log parser is a powerful, versatile tool that provides universal query access to text-based data such as log files, XML files and CSV files, as well as key data sources on the Windows operating system such as the Event Log, the Registry, the file system, and Active Directory”.  

Log Parser is a command line (yes, command line!) tool that uses a SQL dialect to extract information from data sources.  In particular, I have found it to be invaluable for extracting information from the web server logs of the sites that I manage and develop.

First, about that SQL syntax Log Parser uses to query the data sources… many developers seem to have a natural aversion to SQL.  In addition, many new data access frameworks attempt to abstract SQL away from the developer.  However, I have always found SQL easy to work with and believe it to be an essential tool that every developer should at least have a working knowledge of.   For Log Parser, all that is necessary is a basic understanding of the core SQL SELECT statement, as implemented within Microsoft’s SQL Server (that is, T-SQL).  That means you should be familiar with the following elements of a SELECT statement: TOP, FROM, INTO, WHERE, ORDER BY, GROUP BY.  That’s all you need to perform most Log Parser operations.

Curiously, Log Parser has never received the amount of attention that I think it deserves.  Beyond a flurry of attention when it was first released, it seems to be mentioned rarely in official Microsoft communications or blogs.  Despite that, it remains a viable and valuable tool for parsing not just web server log files, but all types of structured text-based data.

In this post, rather than explaining how to use Log Parser. I’ll give a number of examples of its use.  In addition, I’ll document some useful locations where Log Parser information can be found on the web.

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How to setup an SFTP server on CentOS

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:

Run:

rpm -qa|grep ssh

The output should be similar to this:

[root@localhost ~]# rpm -qa|grep sshlibssh2-1.4.3-10.el7_2.1.x86_64openssh-7.4p1-13.el7_4.x86_64openssh-server-7.4p1-13.el7_4.x86_64openssh-clients-7.4p1-13.el7_4.x86_64

That’s all, now we’ll go on how to make the SFTP configuration.

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How to set DNS in CentOS/RHEL 7 & prevent NetworkManager from overwriting /etc/resolv.conf?

This guide shows you how to set custom DNS entries for CentOS 7 / RedHat 7 and ensure that the settings are persistent even after a reboot.

What you need

  • A CentOS 7 or a Red Hat Enterprise Linux (RHEL) 7 server
  • A couple of minutes

Overview

In CentOS and Red Hat Enterprise Linux (RHEL) 7, any custom DNS entries are stored in the file /etc/resolv.conf. However, if we simply go ahead and add our nameservers to this file, we’ll notice that after a reboot or a restart of the network.service, the file is overwritten by NetworkManager.

In this guide, we will first configure NetworkManager to not overwrite this file. Then, we will go ahead and actually add our custom nameservers to /etc/resolv.conf.

Step 1

The NetworkManager configuration is located here: /etc/NetworkManager/NetworkManager.conf Open this file using vim or your favorite text editor.

Search for the [main] section in this file. It should look something like this:

...
[main]
#plugins=ifcfg-rh,ibft
...

Add dns=none just after the [main] tag like this:

...
[main]
dns=none
#plugins=ifcfg-rh,ibft
...

Go ahead and save the file.

Step 2

Let’s restart the NetworkManager.service service so that it picks up the changes we made to the configuration.

sudo systemctl restart NetworkManager.service

Note that the service name NetworkManager.service is case-sensitive.

Step 3

Now, let’s add our nameservers to /etc/resolv.conf

Open this file in you favorite text editor and specify the name servers as follows:

# Generated by NetworkManager
nameserver 8.8.8.8
nameserver 8.8.4.4

That’s it! You’re done. The nameservers added to /etc/resolv.conf will now persist even after a reboot. NetworkManager will not longer overwrite this file.

Centos curl ssl 替换 NSS 为 OpenSSL

系统版本是 Centos 6/7 64位。

1、先安装常用的开发环境。

yum groupinstall Development tools

2、编译OpenSSL

1.下载 OpenSSL:

wget https://www.openssl.org/source/openssl-1.0.2l.tar.gz

2.解压 OpenSSL:

tar -xzvf openssl-1.0.2l.tar.gz

3.进入 OpenSSL目录:

cd openssl-1.0.2l

4.配置并编译 OpenSSL:

./config –shared
make && make install

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The Mega Guide To Harden and Secure CentOS 7

This tutorial only covers general security tips for CentOS 7 which can be used to harden the system. The checklist tips are intended to be used mostly on various types of bare-metal servers or on machines (physical or virtual) that provides network services.

Security and Hardening of CentOS 7

Security and Hardening of CentOS 7

However, some of tips can be successfully applied on general purpose machines too, such as Desktops, Laptops and card-sized single-board computers (Raspberry Pi).

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Enforce Password Complexity Policy On CentOS 7/RHEL Derivatives

In this guide, we are going to learn how to enforce password complexity policy on CentOS 7/RHEL based derivatives. Our previous guide covered the enforcement of password complexity on Ubuntu 18.04. You can check the same by following the link below;

Enforce Password Complexity Policy On CentOS 7

Similar to our previous guide, we are going to use PAM pwquality modules to enforce password complexity policy on CentOS 7/RHEL based derivatives.

In Ubuntu or Debian based derivatives, we modified the, /etc/pam.d/common-password configuration file. For CentOS 7 or similar derivatives, the /etc/security/pwquality.conf or /etc/pam.d/system-auth configuration file is used.

As our normalcy, make a backup of the configuration file before making changes just in case things go south.

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iCACLS使用说明

iCACLS.exe (2003 sp2, Vista+)

Change file and folder permissions – display or modify Access Control Lists (ACLs) for files and folders.
iCACLS resolves various issues that occur when using the older CACLS & XCACLS

Syntax
   Add or remove permissions:
      ICACLS Name
         [/grant[:r] User:Permission[...]]
            [/deny User:Permission[...]]
               [/remove[:g|:d]] User[...]]
                  [/inheritance:e|d|r ]
                     [/setintegritylevel Level[...]]
                        [/T] [/C] [/L] [/Q]

   Store ACLs for one or more directories matching name into aclfile for later use with /restore:
      ICACLS name /save aclfile [/T] [/C] [/L] [/Q]
    
   Restore ACLs to all files in directory:
      ICACLS directory [/substitute SidOld SidNew [...]]
          /restore aclfile [/C] [/L] [/Q]

   Change Owner:
      ICACLS name /setowner user [/T] [/C] [/L] [/Q]

   Find items with an ACL that mentions a specific SID:
      ICACLS name /findsid Sid [/T] [/C] [/L] [/Q]

   Find files whose ACL is not in canonical form or with a length inconsistent with the ACE count:
      ICACLS name /verify [/T] [/C] [/L] [/Q]
 
   Replace ACL with default inherited acls for all matching files:
      ICACLS name /reset [/T] [/C] [/L] [/Q]
   This is equivalent to “Replace all child permission entries with inheritable permission from this object” in the GUI.

Key
   name  The File(s) or folder(s) the permissions will apply to.

   /T  Traverse all subfolders to match files/directories. This will apply permission changes to
       all subfolders whether or not they are set to inherit permissions from the parent. On very large
       directory structures this may take some time as the command has to traverse the entire tree.
   
   /C  Continue on file errors (access denied) Error messages are still displayed.
  
   /L  Perform the operation on a symbolic link itself, not its target.

   /Q  Quiet - supress success messages.

   /grant :r user:permission
       Grant access rights, with :r, the permissions
       will replace any previouly granted explicit permissions (for the given user).
       Otherwise the permissions are added.

   /deny user:permission
       Explicitly deny the specified user access rights.
       This will also remove any explicit grant of the 
       same permissions to the same user.

   /remove[:[g|d]] User 
       Remove all occurrences of User from the acl. 
       :g remove all granted rights to that User/Sid.
       :d remove all denied rights to that User/Sid.

   /inheritance:e|d|r
          e - Enable inheritance
          d - Disable inheritance and copy the ACEs 
          r - Remove all inherited ACEs

   /setintegritylevel [(CI)(OI)]Level 
       Add an integrity ACE to all matching files. 
       level is one of L,M,H (Low Medium or High)

             Mandatory Label\Low Mandatory Level    = Low.
             Mandatory Label\Medium Mandatory Level = Medium/Standard.
             Mandatory Label\High Mandatory Level   = Elevated.

             If No mandatory label is displayed in the output, it is Medium by default. 

       A Directory Inheritance option for the integrity ACE can precede the level
       and is applied only to directories:

   user   A user account, Group or a SID

   /restore  Apply the acls stored in ACLfile to the files in directory

   permission is a permission mask and can be specified in one of two forms:
        a sequence of simple rights:
                D - Delete access
                F - Full access (Edit_Permissions+Create+Delete+Read+Write)
                N - No access
                M - Modify access (Create+Delete+Read+Write)
                RX - Read and eXecute access
                R - Read-only access
                W - Write-only access
        a comma-separated list in parentheses of specific rights:
                DE - Delete
                RC - read control
                WDAC - write DAC
                WO - write owner
                S - synchronize
                AS - access system security
                MA - maximum allowed
                GR - generic read
                GW - generic write
                GE - generic execute
                GA - generic all
                RD - read data/list directory
                WD - write data/add file
                AD - append data/add subdirectory
                REA - read extended attributes
                WEA - write extended attributes
                X - execute/traverse
                DC - delete child
                RA - read attributes
                WA - write attributes
        inheritance rights can precede either form and are applied
        only to directories:
                (OI) - object inherit
                (CI) - container inherit
                (IO) - inherit only
                (NP) - don’t propagate inherit
                (I)  - Permission inherited from parent container
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Linux下进程/程序网络带宽占用情况查看工具 — NetHogs

{“type”:”block”,”srcClientIds”:[“9592bfc1-75c1-490c-ae11-999e86836b85″],”srcRootClientId”:””}nethogs命令

有很多适用于Linux系统的开源网络监视工具。比如说,你可以用命令iftop来检查带宽使用情况。netstat用来查看接口统计报告,还有top监控系统当前运行进程。但是如果你想要找一个能够按进程实时统计网络带宽利用率的工具,那么NetHogs值得一看。

NetHogs是一个开源的命令行工具(类似于Linux的top命令),用来按进程或程序实时统计网络带宽使用率。

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