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% CentOS Download, Installation, and Configuration % Ian! D. Allen - <idallen@idallen.ca>
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- [www.idallen.com] % Winter 2014 - January to April 2014 - Updated Mon Apr 14 16:32:25 EDT 2014 Overview for CentOS Installation ================================ - You will create a VMware Workstation Virtual Machine running a minimal server-style installation of Linux CentOS version 6.5 (\~324MB minimal installation, no GUI) using the instructions below. This is *not* a Desktop system. - For full information on this minimal installation, read the [CentOS MinimalCD 6.5 Release Notes]. - [CentOS] creates versions of Red Hat Enterprise Linux, with Red Hat trademarks and images removed to allow free distribution. They recently became partners with Red Hat “to provide a common platform for open source community project needs”. - Installing and configuring a server (not Desktop) CentOS operating system requires significant Linux expertise. You may not initially know the meaning of all the instructions you must follow, below. By the end of the course, you will know what everything means. - Failure to follow these instructions exactly may lead to future penalties, as we need the exact configuration listed here. - Do not install extra packages or software in this CentOS virtual machine. If you want to experiment, create a separate non-course clone to use. > If you want to play with an easy-install desktop version of Linux, don’t do > it using the system you will install in this document. This document > installs a *server* system, not a *Desktop* system. A Desktop system should > be something graphical and desktop-friendly such as [Ubuntu] or [Mint]. > You can’t use the CentOS system in this document as a Desktop system. This > document is configuring a minimal, non-GUI, **server** version of Linux. Using Other Virtualization Software ----------------------------------- You can use any virtualization software you like to create and run this server-style CentOS virtual machine, e.g. VirtualBox, Parallels, etc., but faculty only fully support questions about **VMware** (and maybe **VirtualBox**). It’s what we know. It isn’t the virtualization software that’s important; it’s the running CentOS virtual machine. I don’t recommend running CentOS directly on your hardware; you lose all the snapshot and backup features available in a Virtual Machine. Don’t do it. Download `CentOS-6.5-i386-minimal.iso` ====================================== > You can start this ISO download process and wait for it to finish while you > move on to the next step to [Create an Empty Virtual Machine] In this section, you will download the `CentOS-6.5-i386-minimal.iso` to your machine. It **must** be the `CentOS-6.5-i386-minimal.iso`, no other version is acceptable for this server. You can get the `CentOS-6.5-i386-minimal.iso` image from one of the following places. We recommend that you choose the first one if you are on campus; it’s the fastest one. Download Method 1 (best): From the CSTECH Downloads Folder ---------------------------------------------------------- This method only works on the Algonquin campus. **Use a wired connection to download big files such as ISO images; don’t use wireless!** 1. On your laptop use a browser to go to the Web site
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<http: cstech>
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on campus. (This only works **ON CAMPUS**!) 2. Choose any room from the left side-bar (e.g. T108). Go to **Drivers and Downloads**, **Linux**, **CentOS**, [**CentOS-6.5-i386-minimal.iso**] 3. Choose exactly this `339738624`-byte ISO file: [`CentOS-6.5-i386-minimal.iso`] 4. Also download the [`CentOS-6.5-i386-minimal.iso-md5.txt`] file containing the *md5sum* file checksum hash. Download Method 2 (worst): From the Internet (slow) --------------------------------------------------- This is much slower than the above CSTECH method. Use it only if you have to: 1. Don’t use this method – it’s slower than the CSTECH method, above. 2. On your laptop use a browser to go to the Web site
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<http: www.centos.org />. 3. Select the **Get CentOS Linux Now** button. 4. Near the bottom of the **Download CentOS** page, find the **Minimal Install Images** section and choose the **More Information** link. 5. In the **Introduction** section, choose the **32-bit** **i386** link
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<http: isoredirect.centos.org centos 6 isos i386 /> 6. Pick a nearby HTTP mirror from the list of `/i386/` mirrors. 7. In the **Index of `/centos/6.5/isos/i386`** find the ISO named `CentOS-6.5-i386-minimal.iso` to download: 8. Choose exactly this `339738624`-byte (324MB) ISO file: `CentOS-6.5-i386-minimal.iso` 9. Also download the `md5sum.txt` file containing the *md5sum* file checksum hashes. Verify the Downloaded ISO ------------------------- To verify the downloaded ISO, you must get a copy of the checksum file from the same CentOS folder where you found the i386 (32-bit) ISO image. 1. Verify that you have the exact ISO file named `CentOS-6.5-i386-minimal.iso` that is 339,738,624 bytes (324MB). 2. To verify the download, you will need some form of checksum program that runs on your local computer that can calculate **md5** or **sha** hashes. Unix/Linux/OSX machines already have the `md5sum` command available (sometimes called just `md5` on OSX); you don’t need to download anything; read the `man` page or just run `md5sum` (or `md5`) followed by the ISO image name and compare the number with the number saved in the checksum hash file. For Windows users, one suggestion to use (thanks Richard!) is [**HashTab**]: a. Windows only: Download and install [**HashTab**] for Windows. (Unix/Linux/OSX users don’t need this program.) b. Copy the desired checksum hash to the clipboard (e.g. from the `md5sum.txt` file). c. Right click in the file you wish to verify, i.e. select your ISO image `CentOS-6.5-i386-minimal.iso` d. Click **Properties** and then **file hashes**. - It will compare the hashes to the one(s) in your clipboard. - MD5 and SHA-1 are the defaults, but it can be customized to include others. 3. Verify the checksum hash of the ISO file against the checksum hash recorded in any of the checksum files located in the same folder. (For example, open `md5sum.txt` and locate the checksum for your ISO file and compare it with the checksum of the ISO file you downloaded.) > Sysadmin Tip for Windows users: You can install the free [**Cygwin**] > package on your own Windows laptop to get BASH and all the Unix tools for > Windows, including `md5sum`, `find`, etc. MacOSX users already have most of > the tools installed and available in any **Terminal** window. Create an Empty Virtual Machine in VMware ========================================= These detailed instructions are for **VMware** Workstation Version 10. You may use any other virtualization software you like (e.g. **VirtualBox**), but you’re on your own if things go wrong. In this section, you will first create an empty Linux **32bit** CentOS-compatible Virtual Machine with no operating system installed. You can do this while you are waiting for your CentOS minimal `CentOS-6.5-i386-minimal.iso` to download. VMware Workstation will try to guide you into an “Easy” or automatic install; you must *not* do an Easy/automatic install. **Do *not* let VMware use “Easy Install”!** 1. Start VMware on your machine. Any version of VMware since Version 8 should work. These instructions were prepared with Version 10. 2. Choose **Create a New Virtual Machine** or **File | New Virtual Machine**. 3. **Welcome to the New Virtual Machine Wizard:** Choose **Typical (recommended)**. - **Typical** asks fewer questions than the full **Custom** install 4. **Guest Operating System Installation:** Select: **I will install the operating system later** - “The virtual machine will be created with a blank hard disk.” - Do *not* let VMware use “Easy Install”! - *Do **not** let VMware use “Easy Install”!* - **Do *not* let VMware use “Easy Install”!** 5. **Select a Guest Operating System:** Select: **Linux**, Version **CentOS** - **Do *not* choose 64 bit!** - If the installation is asking you to create a userid for this step, then you need to start over: **Do *not* let VMware use “Easy Install”!** 6. **Name the Virtual Machine:** If your course and term is **CST8207** and **14W**, then use the name `CST8207-14W-CentOS-6.5` (no spaces). - You may want to change the **Location** if you keep your VMware images in a different folder on your host machine, otherwise leave **Location** unchanged. - You can invent your own virtual machine name, if you prefer. 7. **Specify Disk Capacity:** Enter **2** GB (actually type the number `2` into the box) - If asked, say: **Store virtual disk as a single file (Monolithic)** Under the **Ready to Create Virtual Machine** screen, confirm these important settings: Operating System: CentOS Hard Disk: 2 GB, Monolithic Memory: 1024 MB 8. Finish. You will see **Virtual Machine Created**. 9. Close the New Virtual Machine Wizard. 10. In the VMware **VM | Settings | Hardware** page for this virtual machine: a. Select the **Sound Card** and un-check everything. b. Select the **USB Controller** and un-check everything. c. Select **Save** or **OK**. To confirm your settings: In VMware, select menu **VM | Settings** to open **Virtual Machine Settings** and look under the **Hardware** tab to confirm: Memory: 1024 MB (or 1GB) Processors: 1 Hard Disk: 2GB In the same **VM | Settings** window (“**Virtual Machine Settings**”), go to the **Options | General** tab and confirm: Guest Operating System: Linux Version: CentOS If you don’t see the above settings, delete this virtual machine and start over. Install The Operating System ============================ After you have downloaded and verified the checksum of the 32-bit ISO file `CentOS-6.5-i386-minimal.iso`, you can next follow these instructions below to install this minimal 32-bit CentOS ISO image into your empty CentOS virtual machine that you just created above. 1. The installation software requires more memory than the running CentOS server. If you are installing or re-installing your system, set your VM Memory to **1024MB** (1 GB) before you continue. 2. Connect your downloaded and checksum-verified `CentOS-6.5-i386-minimal.iso` ISO to your VMware virtual CD/DVD drive using the **VM | Settings**, **Hardware | CD/DVD** device page: a. On the CD/DVD device page, under **Device Status** check **Connect at power on**. b. On the CD/DVD device page, select radio button **Use ISO image file:** and browse to the location of your downloaded CentOS ISO file and select it and **Open** it. c. Select **Save** or **OK**. 3. With the downloaded CentOS ISO connected to the CD/DVD of your virtual machine, in your VMware Workstation screen select **Power on this Virtual Machine** or **Start up this guest operating system**. You should see a blue CentOS 6 screen with the title “Welcome to CentOS 6.5!” and five menu entries: ![CentOS 6 Welcome] 4. Put aside your mouse for the moment – the next few configuration steps must be done using the keyboard: a. The first menu entry **Install or upgrade an existing system** is the one that will be chosen as the “Automatic boot” when the 60-second time-out expires. You can use the keyboard **Up/Down** arrow keys to move the cursor up and down to stop the time-out or choose some other menu entry. b. Use the arrow keys to choose the first menu entry **Install or upgrade an existing system** and push **Enter**. (This will happen automatically when the 60-second time-out occurs.) c. Watch many Linux kernel messages stream by in black-and-white. 5. You will see a text screen titled “Welcome to CentOS for i386” containing a box titled `Disc Found` and asking you if you want to test the media. a. In “Disc Found” use the Space bar to select the OK choice. You will see another box titled “Media Check”. b. In “Media Check” use the Space bar to select “Test”. The result must be “Success” or else your ISO file is corrupt and needs to be removed and downloaded again. c. In “Success” use Space to select “OK”. You will see a box saying “Media ejected”. This is dumb. Now we have to reconnect the ISO file! d. Release your cursor from the virtual machine and go back to the VMware **VM | Settings**, **Hardware | CD/DVD** device page: i. Under the CD/DVD **Device Status** section check **Connected**. ii. Select **Save** or **OK**. iii. Go back to your CentOS virtual machine console. iv. (You can also connect the CD using right-click on the CD/DVD icon in the bottom right and select “Connect”.) e. After re-connecting the CD, go back to the “Media ejected” box and use Space to select OK. You will see another “Media Check” box asking you about testing additional media. Make sure the ISO file is connected to your CD/DVD before you continue from this step. f. In this “Media Check” box, use the TAB key to select “Continue” and then the Space bar to activate Continue. It should say “Media detected” and “Found local installation media” and then you should see a graphical CentOS 6 screen with a “Next” button on it (see below). a. If it says “**Error**” and it can’t find the CentOS installation disc, you forgot to reconnect the ISO file to your CD/DVD device, above. Connect the ISO and try again. b. If you only see a blue/gray text screen saying “**Welcome to CentOS!**”, you forgot to increase the Memory to 1024MB for the installation. Power off, do that, and try again. ![CentOS 6 Splash Screen] 6. On the CentOS 6 page, the mouse is working again. Use it or Space to select the Next button. You should see a “What language” page. 7. On the “What language” page use the default English selection. (You may be tempted to chose your own non-English language, but if you do so your Instructor will not be able to help you with any problems. Always use the default English language.) Select Next. 8. On the “Select the appropriate keyboard” page use the default “U.S. English” keyboard. Select Next. 9. On the “What type of devices” page use the default “Basic Storage Devices”. Select Next. 10. On the “Storage Device Warning” page select “Yes, discard any data”. (If you are re-installing your system, you will instead see here an “At least one existing installation” page that asks you to either overwrite or upgrade your existing installation. Choose appropriately.) 11. On the “Please name this computer” page: a. For **Hostname:** enter your eight-character Algonquin Blackboard userid (all lower-case). b. Select Next. 12. On the “Please select the nearest city” page: a. Turn *off* “System clock uses UTC”. Un-check this box. b. Do not change the city. c. Select Next. 13. On the “The root account” page enter (twice) a `root` account [password that you can remember]. Keep it simple – this is a low-security student course machine and not a high-security bank! Select Next. 14. On the “Which type of installation” page select “Create Custom Layout”. We are going to use a simple two-partition system instead of the default (and more complex) Logical Volume Manager layout. Select Next. 15. On the “Please Select A Device” page click on the “Free 2047” line then click on “Create”. (If you are re-installing your system, you will first need to select each existing partition and Delete it to make the free space.) a. On the “Create Storage” page use the default “Standard Partition” then click on “Create”. b. On the “Add Partition” page: i. Use the drop-down list for “Mount Point:” and select `/` (the ROOT). ii. Leave the “File System Type” as `ext4`. iii. Type `1500` into the “Size (MB)” box. iv. Check “Force to be a primary partition” v. Select “OK”. c. You should now have a ROOT (`/`) partition of type `ext4` size 1500 on `sda1`. Delete this partition and start over if this is not true. 16. On the “Please Select A Device” page click on the “Free 547” line then click on “Create”. a. On the “Create Storage” page use the default “Standard Partition” then click on “Create”. b. On the “Add Partition” page: i. Ignore the Mount Point. ii. Change the “File System Type” to `swap`. iii. Ignore the “Size (MB)” box. iv. Check “Fill to maximum allowable size” v. Check “Force to be a primary partition” vi. Select “OK”. c. You should now have a swap partition on `sda2` size 547. Delete this partition and start over if this is not true. ![CentOS 6 Partitions] 17. After confirming the above two partitions and sizes, on the “Please Select A Device” page click on “Next”. 18. On the “Format Warnings” page click “Format”. This completely wipes your Linux virtual disk, not your host machine’s disk. 19. On the “Writing storage configuration to disk” page click “Write changes to disk”. 20. On the “Install boot loader page” page leave the default setting checked (“Install boot loader on `/dev/sda`”) and click “Next”. It should say “Installation starting”. 21. You should see a progress bar saying “Packages completed” as exactly 204 CentOS packages are installed into the system. (If the number is not exactly 204, you are using the wrong ISO image.) The 204-package installation should take about five minutes. ![CentOS 6 Install Packages] 22. On the “Congratulations, your CentOS installation is complete” page select “Reboot”. Some Linux kernel shutdown messages will print, then the virtual machine will reboot. 23. The system should reboot into a black login screen with the banner `CentOS release 6.5 (Final)` and a login prompt preceded by the hostname of the machine, similar to this: CentOS release 6.5 (Final) Kernel 2.6.32-431.el6.i686 on an i686 abcd0001 login: The machine name in front of the `login:` prompt should be your own Blackboard userid, not `abcd0001`. Verify Correct CentOS Installation ---------------------------------- 1. Log in on the black text console as the user `root` with the password that you remembered from the above installation. - If the login doesn’t work, go back and read all the words in the previous sentence, especially the words starting with the letter `r`. Run the following installation verification commands. Your CentOS installation must pass all of the following verification steps: 2. Run: `hostname` and verify that it prints your eight-character Blackboard userid as the machine name. 3. In file `/etc/sysconfig/network` verify that the `NETWORKING` variable is set to `yes` and the `HOSTNAME` variable is set to your Blackboard userid. 4. Run: `fdisk -clu` and verify that your Disk `/dev/sda` is `2147 MB` and that the disk partitions `/dev/sda1` and `/dev/sda2` have `1,536,000` and `560,128` blocks (a block is 1024 bytes). It should look almost exactly like the following, except your machine name and `Disk identifier` number will differ: [root@abcd0001 ~]# fdisk -clu Disk /dev/sda: 2147 MB, 2147483648 bytes 255 heads, 63 sectors/track, 261 cylinders, total 4194304 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Device Boot Start End Blocks Id System /dev/sda1 * 2048 3074047 1536000 83 Linux /dev/sda2 3074048 4194303 560128 82 Linux swap / Solaris 5. Run: `rpm -q -a | wc` and verify that you have exactly `204` packages installed. 6. Run: `df -h` and verify that your `/dev/sda1` virtual disk partition mounted on `/` (the ROOT) has a **Size** of `1.5G` (ignore the other sizes – they may differ slightly): [root@abcd0001 ~]# df -h Filesystem Size Used Avail Use% Mounted on /dev/sda1 1.5G 598M 804M 43% / tmpfs 504M 0 504M 0% /dev/shm 7. Run: `swapon -s` and verify that partition `/dev/sda2` is listed as an active swap partition: [root@abcd0001 ~]# swapon -s Filename Type Size Used Priority /dev/sda2 partition 560120 0 -1 You may need to delete this virtual machine and re-install if any of the above numbers or verification steps are wrong. Redo your installation or consult with your instructor if any of the above verification commands don’t give the expected output. Networking is not enabled on this server yet. It is a good idea to configure your system a bit before enabling networking, so we will enable networking later, after doing some configuration. Snapshot your Fresh Installation -------------------------------- Make sure your CentOS virtual machine passes the all above verify steps before saving it! 1. Shut down your CentOS machine by typing: `shutdown -h now` - You will see some Linux kernel messages before the machine halts. - **NEVER** power off a Linux machine using the VMware Power button! - **ALWAYS** power off a Linux machine using `shutdown` or `halt`. 2. In the VMware **VM | Settings | Hardware** page for this virtual machine: a. Change the **Memory** from `1024MB` down to `256MB`. Say OK. - You will need to put Memory back up to 1024MB if you need to re-install the system from CD. - Keeping system memory small (e.g. 256MB) makes snapshots of running systems faster. b. Select the **Sound Card** and un-check everything. (You should have already done this when creating the VM.) c. Select the **USB Controller** and un-check everything. (You should have already done this.) d. Select **Save** or **OK**. 3. Use VMware (or your virtualization software) to create a Snapshot of your new VM. In VMware use **VM | Snapshot | Take snapshot…**. Label the Snapshot **Fresh Minimal Installation** and enter a dated comment explaining how you created it and what installation parameters you used: a. Minimal ISO: `CentOS-6.5-i386-minimal.iso` b. Memory `256MB` c. Disk `2GB` d. Hostname `abcd0001` (should be your Blackboard userid) e. 204 packages f. no network at boot time 4. Open the **VM | Snapshot | Snapshot Manager** to confirm your snapshot. - You will have this snapshot to come back to if you ever need it. 5. If you have taken a successful snapshot, close the snapshot manager. Problems with Snapshots of Running Systems ------------------------------------------ A snapshot of a running (not fully shut down) system is quick to resume if you ever need to go back to it, but a running snapshot has some potentially serious problems: 1. Snapshots take more space if you take them when the machine is running, since the snapshot has to save all the system memory. Snapshots are smaller if you take them of a system that is powered off. 2. Often you need to restore a snapshot and also make some **VM | Settings** changes. If you snapshot a running system, then you have to shut it down every time you restore it when you want to make **VM | Settings** changes. Better to create the snapshot of the powered-off system. 3. A snapshot of a running system can only safely be resumed (restarted) on the system that created it, or a system running a similar CPU type. You cannot safely back-up the running snapshot files onto a different CPU type and resume it there. A snapshot of a running system may be useless if you try to restart it on a different computer, such as might happen if your laptop computer fails and you need to borrow another. When possible, make your important snapshots of virtual machines that are actually powered off. Configure CentOS ================ This configuration section assumes you are starting your configuration from the **Fresh Minimal Installation** snapshot from the previous section. Before you begin, you need to understand some terms. (These few points are not action items; they are for your information.) Make note of these things: A. When it says “*back up a file*” below, it means copy the file, preserving time and owner information, into the *same* directory with a `.bak` suffix on the file name, for example: $ cp -p /foo/bar /foo/bar.bak $ cp -p /some/path/name/file /some/path/name/file.bak You may find this shell alias useful: `alias cp='cp -p -i'`\ but remember that aliases are not saved when the shell exits. Remember to edit the *original* file, not the back-up file. B. When it says “*edit a file*” below, it means use the `vi` (not `vim`) text editor, because that’s the only editor there is. Every Unix/Linux system has `vi` installed. (Servers, including this one, don’t by default install the dumb `nano` editor.) - You need to how to use basic `vi` editor commands to open a file, edit it, and save it do the editing work below. - The editor is named `vi`, not `vim` on CentOS. We will install a full version of `vim` shortly. C. When it says “*comment out*” something below, it means insert a comment character (usually `#`) at the very start of the line, e.g. change `hiddenmenu` to `#hiddenmenu` or change `alias rm='rm -i'` to `#alias rm='rm -i'`. The comment character turns the whole line into a *comment* – something that the program reading the file will ignore. Make the configuration changes below to your **Fresh Minimal Installation** machine. Remember to preserve modification times on all files copied! If you have network connection problems below see [Network Diagnostics]. Boot the Fresh Minimal Installation snapshot -------------------------------------------- 1. Boot (power on) your **Fresh Minimal Installation** snapshot from the previous section. 2. Log in as the `root` user on the black text console, as you did before. 3. Review the above points A., B., and C. so that you know what “*back up*”, “*edit*”, and “*comment out*” mean. 4. Create your alias for `cp` to preserve modify times so that you don’t forget. Enable networking ----------------- Networking is not yet enabled on boot. Enable it, so that you can connect to your CentOS system using a proper SSH connection instead of using the limited VMware system console: 1. Back up the file `/etc/sysconfig/network-scripts/ifcfg-eth0` then edit the original file and change the `ONBOOT` variable setting from `ONBOOT=no` to `ONBOOT=yes`. (Always edit the original file, not the back-up file!) Save the file and exit the editor. - Display the file and make sure `ONBOOT=yes` - Use the `diff` command to compare the back-up file with the new file and make sure only *one* line has changed. 2. At the bash `root` prompt run: `service network restart` - You should now see several lines including two lines for `eth0`:\ `Bringing up interface eth0:` and\ `Determining IP information for eth0... done. [OK]` - If you have network connection problems see [Network Diagnostics]. 3. Confirm that you have a working IP address on `eth0`: a. Run: `ifconfig eth0 | fgrep 'inet addr'` and see one line of output containing your system IP address (your `inet addr`). **Write down this local IP address; you will need it shortly.** b. Run: `ip route | fgrep 'default'` and see one line of output containing your default gateway IP address. c. Run: `ping -c 1` *X.X.X.X* where *X.X.X.X* is your default gateway IP address and look for `0% packet loss`. (This may not work if you are using Bridged networking on-campus at Algonquin College because the ITS department blocks `ping`.) Sample output for the above commands is given below – your hostname and CentOS IP addresses (write it down) will differ: [root@abcd0001 ~]# fgrep 'ONBOOT' /etc/sysconfig/network-scripts/ifcfg-eth0 ONBOOT=yes [root@abcd0001 ~]# service network restart Shutting down loopback interface: [ OK ] Bringing up loopback interface: [ OK ] Bringing up interface eth0: Determining IP information for eth0... done. [ OK ] [root@abcd0001 ~]# ifconfig eth0 | fgrep 'inet addr' inet addr:192.168.9.141 Bcast:192.168.9.255 Mask:255.255.255.0 [root@abcd0001 ~]# ip route | fgrep 'default' default via 192.168.9.254 dev eth0 [root@abcd0001 ~]# ping -c 1 192.168.9.254 PING 192.168.9.254 (192.168.9.254) 56(84) bytes of data. 64 bytes from 192.168.9.254: icmp_seq=1 ttl=64 time=1.78 ms --- 192.168.9.254 ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 2ms rtt min/avg/max/mdev = 1.780/1.780/1.780/0.000 ms Make sure the `ping` shows `0% packet loss` (unless you are at Algonquin College, using Bridged networking, and `ping` is being blocked by ITS, sorry). Did you write down your CentOS IP address (not your default gateway address)? You are about to use it. Use an SSH connection instead of the console -------------------------------------------- You may find it easier to use and configure your CentOS system using an SSH terminal connection that you can resize and in which you can use copy/paste instead of the fixed-size VMware CentOS console that you cannot resize or use copy/paste. > Sometimes the networking set-up on your host operating system does not > permit you to connect to the network addresses of your virtual machines. If > that is true, the following won’t work and you’ll have to consult the > manual for your host operating system on how to enable network access to > virtual machines. 1. In your host operating system (not in the CentOS guest OS), create an SSH remote connection to the CentOS IP address for your machine that you wrote down in the previous step. (This IP address was listed beside the output for `inet addr` for `eth0`.) - Review the instructions on how to do a [Remote Login] to the [Course Linux Server], but do not use any of your saved CLS connection information. Create a new SSH connection with the (above) new CentOS IP address. - Connect via SSH using **PuTTY** on Windows, or use `ssh` on Macintosh or Linux. - If you have saved CLS settings in your connection program, do not use your CLS settings; create new settings. - Log in to your CentOS machine (not the CLS) as `root` with your `root` password. Make sure you are using your CentOS address. - Do not try to log in as `root` to the CLS! The CLS will lock out your IP address! Log in to **your** CentOS machine using **your** CentOS IP address! 2. Once you are logged in to your own CentOS machine, type `who` and see that `root` is logged in once on a VMware system console (`tty1`) and once remotely via an SSH *pseudo-terminal* (`pts/0`). [root@abcd0001 ~]# who root tty1 2014-03-09 23:26 root pts/0 2014-03-09 01:22 (192.168.244.1) [root@abcd0001 ~]# tty /dev/pts/0 **I recommend using the SSH connection for all sysadmin work (including the rest of this document). Do not use the crappy VMware console. Note that, unlike using the system console, SSH network connections do not survive across a VM Suspend and Restore. All SSH sessions active when you suspend your VM will be disconnected. Save and exit your editors that are running over SSH before you suspend.** Install the `man` command ------------------------- This system has manual pages, but no `man` command to view them: [root@abcd0001 ~]# which man /usr/bin/which: no man in (/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin) [root@abcd0001 ~]# whereis man man: /usr/share/man Use the `yum` install command to fetch information about the `man` package, and then we will install it: 1. As `root` run: `yum info man` - The first time you do this, `yum` will download some package lists before it answers the `info` query. - If `yum` cannot connect to the Internet, see [Network Diagnostics]. - If `yum` seems to hang for a long time, see [Appendix I]. 2. Confirm that `yum` shows `Name : man` under `Available Packages`. - If you see `man` under `Installed Packages`, you have already installed it. 3. Run: `yum install man` and when it asks `Is this ok [y/N]:` answer with `y` (yes) and *Enter*. - The first time you do this, `yum` will also ask you to import a GPG **CentOS 6 Official Signing Key**. Answer with `y` (yes). 4. Make sure `which man` and `whereis man` and `man man` now work: [root@abcd0001 ~]# which man /usr/bin/man [root@abcd0001 ~]# whereis man man: /usr/bin/man /etc/man.config /usr/share/man /usr/share/man/man1/man.1.gz [root@abcd0001 ~]# man man ...etc... Install the `mail` command -------------------------- Servers often need to email status messages to humans. We need to use the `yum` install command to fetch and install an email client program package named `mailx`: 1. As `root` run: `yum info mailx` - The first time you do this, `yum` will download some package lists before it answers the `info` query. - If `yum` cannot connect to the Internet, see [Network Diagnostics]. - If `yum` seems to hang for a long time, see [Appendix I]. 2. Confirm that `yum` shows `Name : mailx` under `Available Packages`. - If you see `mailx` under `Installed Packages`, you have already installed it. 3. Run: `yum install mailx` and when it asks `Is this ok [y/N]:` answer with `y` (yes) and *Enter*. - The first time you do this, `yum` will also ask you to import a GPG **CentOS 6 Official Signing Key**. Answer with `y` (yes). 4. After installation, make sure that `mail -V` (upper case!) prints a version number (the number may differ, depending on which version of CentOS is installed): [root@abcd0001 ~]# mail -V 12.4 7/29/08 The `mailx` package installs some symbolic links so that the command `mail` actually runs the `mailx` program: [root@abcd0001 ~]# ls -l /bin/mail* lrwxrwxrwx. 1 root root 22 Mar 9 22:16 /bin/mail -> /etc/alternatives/mail -rwxr-xr-x. 1 root root 369440 Aug 1 2013 /bin/mailx [root@abcd0001 ~]# ls -l /etc/alternatives/mail lrwxrwxrwx. 1 root root 10 Mar 9 22:16 /etc/alternatives/mail -> /bin/mailx Also `man mail` gives you the same `man` page as `man mailx` (again using more symlinks): [root@abcd0001 ~]# whereis mail mailx mailx: /bin/mail /etc/mail.rc /usr/share/man/man1/mail.1.gz mailx: /bin/mailx /usr/share/man/man1/mailx.1.gz [root@abcd0001 ~]# ls -l /usr/share/man/man1/mail.1.gz lrwxrwxrwx. 1 root root 31 Mar 9 22:16 /usr/share/man/man1/mail.1.gz -> /etc/alternatives/mail-mail-man [root@abcd0001 ~]# ls -l /etc/alternatives/mail-mail-man lrwxrwxrwx. 1 root root 30 Mar 9 22:16 /etc/alternatives/mail-mail-man -> /usr/share/man/man1/mailx.1.gz Install the full version of the `vim` editor -------------------------------------------- Your CentOS **Minimal Installation** comes with a *minimal* (they call it `Small`) version of the `vim` text editor named `vi` that is missing many features and help files: [root@abcd0001 ~]# vi --version | fgrep 'version' Small version without GUI. Features included (+) or not (-): [root@abcd0001 ~]# vimtutor -bash: vimtutor: command not found We want the full version, with help files and tutorials. As `root`, download and install the full (they call it `Huge`) version of `vim` as follows: 1. As `root` run: `yum info vim-enhanced` - The first time you do this, `yum` will download some package lists before it answers the `info` query. - If `yum` cannot connect to the Internet, see [Network Diagnostics]. - If `yum` seems to hang for a long time, see [Appendix I]. 2. Confirm that `yum` shows `Name : vim-enhanced` under `Available Packages`. - If you see `vim-enhanced` under `Installed Packages`, you have already installed it. 3. Run: `yum install vim-enhanced` and when it asks `Is this ok [y/N]:` answer with `y` (yes) and *Enter*. - The first time you do this, `yum` will also ask you to import a GPG **CentOS 6 Official Signing Key**. Answer with `y` (yes). - You will note under **Installing for dependencies** a list of other packages on which the full version of VIM depends. All this software also has to be downloaded and installed with VIM, including the **Perl** interpreter and some libraries. - Downloading all the software will take a minute or two. 4. After successful download and installation, start the newly-installed full version of VIM by typing `vim` (not `vi`) and note that this is the *Huge* version: [root@abcd0001 ~]# vim --version | fgrep 'version' Huge version without GUI. Features included (+) or not (-): [root@abcd0001 ~]# which vimtutor /usr/bin/vimtutor 5. The programs `vi` and `vim` are different in CentOS! - You may find some accounts come with an alias: `alias vi=vim` - In which system directory is the minimal (`Small`) `vi` program found? - In which system directory is full (`Huge`) enhanced `vim` program found? - What system command makes it easy to answer the above two questions? Remove confusing and dangerous `root` aliases --------------------------------------------- CentOS has provided the `root` account with some personal shell aliases that change the behaviour of some important commands and this is a bad idea. Type `alias` and you will see some aliases similar to these: [root@abcd0001 ~]# alias alias cp='cp -i' alias l.='ls -d .* --color=auto' alias ll='ls -l --color=auto' alias ls='ls --color=auto' alias mv='mv -i' alias rm='rm -i' alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde' The aliases for `ls` and `which` are harmless, but the options added in the aliases for `cp`, `mv`, and `rm` change the behaviour of these commands significantly. (What do those options do? RTFM for each command.) On real servers, the `root` account is often shared among several sysadmin, and so you must *not* define your own personal aliases in the `root` account. Commands must work exactly as expected, not the way aliases might change them to work. We will remove these dangerous aliases from our `root` account: 1. Back up the file `/root/.bashrc` (preserve the modify time) then edit the original file: a. Remove or comment out the alias for `rm`. b. Remove or comment out the alias for `cp`. c. Remove or comment out the alias for `mv`. 2. In addition to making the above essential changes, you might also optionally add `unalias -a` to make sure that no misleading aliases are defined for the `root` account. - Add this `unalias` line at the *bottom* (end) of the `.bashrc`, *after* all the existing lines in the file. - Use the `diff` command to compare the back-up file with the new file and make sure only a few lines have changed. Keep your own personal aliases in your *own* account and `source` them when you need them as `root`. Do **NOT** put your personal aliases into the `root` account itself. (Review [Optional Sysadmin Shell Aliases].) Log out of your VM and then log back in. Type `alias` and make sure all the dangerous aliases are gone. Enable shell History -------------------- Shell command line history for `root` is important to a sysadmin. It’s one way of knowing what commands were typed as `root`. Although the shell is saving its history upon exit, the history from different shells is not being saved, so history can be lost if you run more than one shell (e.g. multiple windows or multiple logins). Also, history is not being saved until a shell exits, which means you can also lose history if a shell is killed prematurely. We will fix this: 1. Confirm that you have already backed up the file `/root/.bashrc` then edit the original file again: a. Insert this line at the top (beginning) of the file: [ -z "${PS1-}" ] && return b. Add these lines at the bottom (end) of the file: # check the window size after each command and update LINES and COLUMNS # append history to history file instead of overwriting it shopt -s checkwinsize shopt -s histappend # keep a lot of shell history # keep time stamps on each entry # update history file after every command (not just on exit) export HISTSIZE=9000 export HISTFILESIZE=99000 export HISTTIMEFORMAT= PROMPT_COMMAND='history -a' c. Save your changes and exit your text editor back to the command prompt. d. Use the `diff` command to compare the back-up file with the new file and make sure only the intended lines have changed. 2. Run `source ~/.bashrc` to source the new file to set up the history in the current shell. Make sure you see no output and no errors! 3. After sourcing the file, print the changed history variables to confirm: [root@abcd0001 ~]# source ~/.bashrc [root@abcd0001 ~]# printenv | fgrep 'HIST' HISTSIZE=9000 HISTFILESIZE=99000 HISTTIMEFORMAT= [root@abcd0001 ~]# echo "$PROMPT_COMMAND" history -a 4. Check that the verification commands you just typed into the shell, above, are appearing at the bottom (end) of the `root` BASH history file `.bash_history`. (What command shows you the last few lines of a text file?) Enable loopback address for your machine name name -------------------------------------------------- The file `/etc/hosts` usually contains a local copy of the name of the current machine, paired with the loopback IP address. CentOS is missing this, which means you can’t `ping` your own host name: [root@abcd0001 ~]# echo "$HOSTNAME" abcd0001 [root@abcd0001 ~]# ping "$HOSTNAME" ping: unknown host abcd0001 1. Back up the file `/etc/hosts` then edit the original file and add your machine’s host name by adding the line `127.0.0.2 abcd0001` where *abcd0001* is replaced by *your* machine’s host name (which must be the same name as your Blackboard userid): [root@abcd0001 ~]# cat /etc/hosts 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 127.0.0.2 abcd0001 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 Use the `diff` command to compare the back-up file with the new file and make sure only the intended lines have changed. 2. Confirm that you can now `ping` your own machine name with zero packet loss: [root@abcd0001 ~]# echo "$HOSTNAME" abcd0001 [root@abcd0001 ~]# ping -c 1 "$HOSTNAME" PING abcd0001 (127.0.0.2) 56(84) bytes of data. 64 bytes from abcd0001 (127.0.0.2): icmp_seq=1 ttl=64 time=0.072 ms --- abcd0001 ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 0.072/0.072/0.072/0.000 ms The name *abcd0001* above must be *your* machine’s name, not `abcd0001`. Your machine name must be the same name as your Blackboard userid. Enable Internet Time using NTP and `ntpd` ----------------------------------------- The system time is not being synchronized with the Internet. We need to use the `yum` install command to fetch and install the Network Time Protocol (NTP) package named `ntp` with its time daemon named `ntpd`: 1. As `root` run: `yum info ntp` - The NTP package is named `ntp`; the NTP daemon is named `ntpd`. - The first time you do this, `yum` will download some package lists before it answers the `info` query. - If `yum` cannot connect to the Internet, see [Network Diagnostics]. - If `yum` seems to hang for a long time, see [Appendix I]. 2. Confirm that `yum` shows `Name : ntp` under `Available Packages`. - If you see `ntp` under `Installed Packages`, you have already installed it. 3. Run: `yum install ntp` and when it asks `Is this ok [y/N]:` answer with `y` (yes) and *Enter*. - The first time you do this, `yum` will also ask you to import a GPG **CentOS 6 Official Signing Key**. Answer with `y` (yes). 4. Back up the file `/etc/ntp.conf` then edit the original file to add the line `tinker panic 0` on its own line just above the `driftfile` line. - Use the `diff` command to compare the back-up file with the new file and make sure only the one line changed. - This line tells the `ntpd` program that it can always change the clock value, no matter how far off it is. Normally the `ntpd` daemon refuses to change a clock value that is more than 1,000 seconds wrong. - This doesn’t always work, and sometimes NTP can’t synchronize your clock inside some versions of VMware or under some host operating systems. Sometimes, installing the VMware Tools package can mitigate this problem; more on that later. 5. Run: `chkconfig --list ntpd` (and note the spelling of the service name `ntpd`). You will see one line indicating that the `ntpd` time daemon is turned **off** in every Run Level. 6. Run: `chkconfig ntpd on` (again note the spelling of `ntpd`). 7. Run: `chkconfig --list ntpd` (again note the spelling of `ntpd`). You will see one line indicating that the `ntpd` time daemon is now turned **on** in Run Levels 2 through 5: [root@abcd0001 ~]# chkconfig --list ntpd ntpd 0:off 1:off 2:on 3:on 4:on 5:on 6:off 8. Run: `service ntpd start` and you should see one line saying `Starting ntpd: [OK]`. (If you already started `ntpd`, you won’t see the `[OK]`.) 9. Run: `tail /var/log/messages` or `fgrep 'ntpd' /var/log/messages` and confirm that there are several log entries for `ntpd` saying `Listen normally`. If you see errors, fix them and run `service ntpd restart` to restart `ntpd`. 10. If all goes well, `ntpd` starting up will have reset your system clock to the correct time. (Run the `date` command and see.) The log file might say something like `clock_step +14398.864481s` indicating a time change of (for example) 14398 seconds. If nothing happened, try waiting 5–10 minutes and see if the time updates. You can perform the other edits below while you wait for this to happen. Continue reading: 11. Installing NTP doesn’t always work to keep your system time updated, and sometimes NTP can’t synchronize your clock inside some versions of VMware or under some host operating systems. Sometimes, installing the VMware Tools package can mitigate this problem; more on that later. Even with `ntpd` running, the system may take 5-10 minutes to re-synchronize its time after a VM Pause, Suspend, or reboot. (Earlier versions of CentOS were faster at time synchronization.) Servers in the real world are not paused, suspended, or rebooted as often as at school. Installing **VMware Tools** will often help with getting the time right after a VM pause or suspend. **VMware Tools** will be installed in a separate document, later. Configure our local Time Zone ----------------------------- The system time zone file is not correct for our time zone. 1. Run: `tzselect` and answer the questions to find the full name of the **Eastern Time – Ontario** time zone. (Hint: It is two words separated by a slash, and has the name `Toronto` in it.) Ignore the advice about your `.profile` file – you are the **sysadmin** of this machine and you are setting the system time zone, not an individual user’s time zone. 2. Back up the file `/etc/sysconfig/clock` then edit the original file to change the `ZONE` variable to `ZONE="XXX/YYY"` where *XXX/YYY* is the name of the time zone printed by `tzselect` (including the double quotes). The word `Toronto` is in this name. 3. Run the `tzdata-update` command. This will copy the correct time zone information file from under directory `/usr/share/zoneinfo/` to `/etc/localtime`. 4. Run a checksum (any kind) on the file `/etc/localtime` and on the file under directory `/usr/share/zoneinfo/` corresponding to the `Toronto` time zone and verify that both files have the same checksum. (Hint: You will need to search for the correct `Toronto` file under that directory. What command finds file names by basename? What command can calculate a checksum?) Disable SELinux --------------- Security Enabled Linux is turned on, which can cause many problems for novice Linux users. On a real server, we would leave it enabled. You will learn SELinux configuration in later Linux courses. 1. Back up the file `/etc/sysconfig/selinux` then edit the original file and change the `SELINUX` variable setting from `SELINUX=enforcing` to `SELINUX=disabled`. - Use the `diff` command to compare the back-up file with the new file and make sure only the one line changed. 2. We won’t check to see that this works until after the next reboot. Disable Pretty Boot ------------------- The system boot messages are being hidden by a pretty but unhelpful CentOS graphics screen. The screen covers up many useful system messages at boot time. As a sysadmin, you *want* to see *all* the boot messages. 1. Take a snapshot of your VM now, in case you make a mistake in the following edit. If you damage lines in this GRUB configuration file, your machine may not boot at all. You’ll have to restore from the snapshot and reconfigure. 2. Back up the file `/boot/grub/grub.conf` then edit the original file: a. Change the value of the `timeout` from `5` to `30`. b. Comment out the `hiddenmenu` line to make the GRUB menu visible on boot. (Insert a single `#` comment character in front of `hiddenmenu` so that it looks like `#hiddenmenu` and will be ignored.) c. Remove the two words `rhgb quiet` from the far right end of the very long `kernel` line to get rid of the silly CentOS animated graphics screen. (Make sure you don’t accidentally break this line into pieces. Keep it one long line.) d. The resulting file should be two words smaller than the back-up file: [root@abcd0001 ~]# wc -lw /boot/grub/grub.conf* 17 81 /boot/grub/grub.conf 17 83 /boot/grub/grub.conf.bak e. Use the `diff` command to compare the back-up file with the new file and make sure only the intended lines have changed. 3. You will know if your edits are accurate at the next reboot, coming up in the next section. If the reboot fails, restore back to your snapshot and try the edit again. Verify Correct CentOS Configuration ----------------------------------- Having made all the above configuration changes, your CentOS configuration must pass all of the following verification steps after you reboot it: 1. Reboot your CentOS machine by typing: `shutdown -r now` or simply `reboot` - If you are using a remote SSH connection, you will be disconnected. - Open up the VMware system console and verify that you now see the GRUB boot menu. 2. Verify the new GNU GRUB boot menu: a. The `GNU GRUB` menu should now be visible (not hidden) – see the image below. b. In 30 seconds the menu will time out and boot the highlighted menu entry (usually the first one), or you can push the **Enter** key to boot it immediately. If you don’t see the GRUB menu, you forgot to edit the GRUB configuration file above (or your edits were wrong). Try again. ![CentOS 6 GRUB Menu] After the boot, when the machine is up and running, log in on the console again (or, better, use an `ssh` or `PuTTY` connection to the IP address) and log in as the user `root` so you can run some verification commands: 3. Run `alias` and make sure the `root` account has no dangerous aliases. 4. Check that the commands you just typed, above, are appearing at the bottom (end) of the `root` BASH history file `.bash_history` and that the history environment variables set in the `root` `.bashrc` are all set in the current shell. 5. Run: `free` and verify that you have a `total` Memory of about 256MB (e.g. approximately `248836KB`). (If you have more than about 256MB, you forgot to change the Memory settings for this VM. Shut it down safely and fix the Memory and reboot.) 6. Run the `selinuxenabled` command followed by `echo "$?"` to display the command exit status variable contents. The status must be `1` (indicating failure – SELinux should not be enabled). If you see zero, you forgot to disable `SELINUX` above. Try again. [root@abcd0001 ~]# selinuxenabled ; echo $? 1 7. In file `/etc/sysconfig/clock` verify that the `ZONE` variable is set to a local Ontario city time zone (not New York). 8. Run: `pgrep -l ntpd` and verify that the output is one line (a process number and the word `ntpd`). - The system can take 5-10 minutes to re-establish the correct time when started or resumed. - Sometimes the time just won’t stay synchronized. We will be installing VMware Tools shortly. 9. Look at the first ten lines of `/etc/ntp.conf` and verify that you find the `tinker panic 0` line you added. 10. Search for the word `ONBOOT` in file `/etc/sysconfig/network-scripts/ifcfg-eth0` and verify that its value is set to `yes`. 11. Run: `ifconfig eth0` and verify that its `inet addr:` has an IP address listed. - If you logged in successfully using an SSH connection, you already know networking is working! 12. Run: `ip route` and verify that you have a `default via` route listed for `dev eth0`. 13. Examine file `/etc/resolv.conf` and verify that there is at least one`nameserver` line in the file. 14. Confirm that you can `ping` your own machine name with zero packet loss and that your host name resolves to the IP loopback address `127.0.0.2`: [root@abcd0001 ~]# ping -c 1 "$HOSTNAME" PING abcd0001 (127.0.0.2) 56(84) bytes of data. 64 bytes from abcd0001 (127.0.0.2): icmp_seq=1 ttl=64 time=0.072 ms --- abcd0001 ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 0.072/0.072/0.072/0.000 ms 15. Make sure the `man` command works. 16. Make sure the `mail` command is installed. 17. Make sure the full `Huge` version of VIM is installed. 18. Run: `rpm -q -a | wc` and verify that you have exactly `220` packages installed. - Do not install any packages other than those required for your course. Consult with your instructor if any of the above verification steps fail. Sometimes you can recover a missed configuration step without starting over from scratch. Snapshot your Configured Installation ------------------------------------- Make sure your CentOS virtual machine passes the all above verification steps before saving it! 1. To avoid all the resume problems mentioned earlier, you may want to [shut down your machine before taking a snapshot]. 2. Use VMware (or your virtualization software) to create a power-off Snapshot of your new **Configured Installation** VM. a) Shut down and power off your machine, so that you don’t have to save the system memory as part of the snapshot. b) Label the Snapshot **Configured Installation** c) Enter a dated comment explaining how you created it and what configuration changes you made (above) from the previous snapshot. Enter one line of comment for every configuration change you made, above. 3. Use **VM | Snapshot | Snapshot Manager** to confirm your snapshot. - You will have this snapshot to come back to if you ever need it. 4. You can delete any intermediate snapshots that you don’t need, leaving only the **Fresh Minimal Installation** and the **Configured Installation**. ![CentOS 6 Configuration Snapshot] Install VMware Tools -------------------- Now, [**Install VMware Tools**] * * * * * This ends the initial Installation and Configuration of a minimal server-style CentOS system. The next sections explain some important things to know about your new virtual server. * * * * * Suspending and Shutting Down Safely =================================== - **NEVER POWER OFF YOUR CENTOS VIRTUAL MACHINE VIA VMWARE POWER OFF!** - Never use the **Power off** button in a virtual machine that you care about! - Never close or kill VMware without first suspending or shutting down all your virtual machines. - Powering off a virtual machine via the VMware power button can corrupt your disk and lose all your work. You can either *Suspend* or *Shut Down* (power off) your VM as follows: Suspending ---------- This is the fastest way to save your machine state. Most times you will want to suspend your Virtual Machine so that you can resume it quickly where you left off: 1. Save any work you are doing over a remote SSH connection. - All SSH connections will be dropped during a *suspend*. 2. Go to **VM** and **Power** and choose **Suspend** 3. Wait until VMware fully saves the state of the machine. 4. You may now safely close VMware. Resuming -------- When you resume your Virtual Machine, you may need to refresh the network settings for your new network location by running (as `root`): `service network restart` Shutting Down (Power Off) ------------------------- If you need to reconfigure most parts of the VMware Virtual Machine that is running your Linux server, you need to shut down Linux before VMware will let you change the settings. Here’s how: 1. Log in as `root` (or login in as a user and then become `root`, if you have disabled `root` logins) 2. Save any work you are doing in the virtual machine. 3. As `root` run: `shutdown -h now` or simply `halt` (if available) - You can also schedule a shutdown at a later time; see the man page. 4. Wait until the Virtual Machine fully shuts down and stops. 5. You may now change VMware settings or safely close VMware. Switching Consoles ================== Most Linux machines running in multi-user mode (not single-user) allow you to have multiple system consoles active by typing `ALT+F2` (hold down `ALT` and simultaneously push `Function Key 2`) to switch to the second console, `ALT+F3` to the next one, etc. The default, first, console is of course `ALT+F1`. This only works on console terminals, not on remote login sessions. Multiple consoles allow you to multi-task and have multiple “windows” on the system console without all the overhead of a graphical user interface. > When you log out of a server console, make sure you check all the alternate > consoles and log them out, too! Don’t leave an open `root` login session > active when you walk away from the machine console! You can’t do `ALT+F2` inside a **PuTTY** or **SSH** session, but there are programs such as [`screen`] and [`tmux`] that let you do that type of multiple console interface and much, much more. * * * * * Appendix I: What to do if `yum` doesn’t work ============================================ This **Appendix** is only necessary if you find that the `yum` installer hangs or does not work. If `yum` hangs or fails, do these steps until it works: 1. If `^C` (`Ctrl-C`) will not interrupt the hung `yum` command, use `^Z` to `STOP` the `yum` command and then `kill %yum` to kill it. (If that doesn’t kill it, use `kill -9 %yum`) a. Another way to kill a hung `yum` session is to switch to a second console (e.g. `ALT-F2`), log in as `root`, find the process ID of the hung `yum` process, use `kill` to send that process ID a `SIGTERM` or `SIGKILL` termination signal, then switch back to the first console again. 2. Make sure your host operating system is **not** using wireless. Change your host O/S to use a wired connection and **disable your wireless** so that it is not used. (Never use wireless if wires are available!) 3. As `root` type: `service network restart` and try `yum` again. - You can try to `ping` hosts, but Algonquin College blocks most ICMP traffic so it may not work as a diagnostic tool. 4. If `yum` still hangs on the wired network, kill `yum` again (see above) and then try: a. Go to **VM | Settings** and **Hardware** and **Network Adapter** b. Change your networking from **Bridged** to **NAT** or from **NAT** to **Bridged** c. Save the new settings. d. Run: `service network restart` and try `yum` again. When `yum` finally works, you may need to accept a security key: say yes * * * * * Appendix II: Document Revision History ====================================== - Version 1: 04:00 Oct 16 2013 - Version 2: 11:45 Oct 16 2013 - put enable networking first - Version 3: 14:20 Oct 16 2013 - check for tinker and 127.0.0.2 - Version 4: 20:15 Oct 17 2013 - clarified some wording; made SSH more prominent - Version 5: 08:00 Feb 16 2014 - added “man” command to system - Version 6: 05:00 Mar 10 2014 - added “mail”, “vim” to system * * * * * -- | Ian! D. Allen - idallen@idallen.ca - Ottawa, Ontario, Canada | Home Page: http://idallen.com/ Contact Improv: http://contactimprov.ca/ | College professor (Free/Libre GNU+Linux) at: http://teaching.idallen.com/ | Defend digital freedom: http://eff.org/ and have fun: http://fools.ca/ [Plain Text] - plain text version of this page in [Pandoc Markdown] format [www.idallen.com]: http://www.idallen.com/ [CentOS MinimalCD 6.5 Release Notes]: http://wiki.centos.org/Manuals/ReleaseNotes/CentOSMinimalCD6.5 [CentOS]: http://www.centos.org/ [Ubuntu]: http://ubuntu.com/ [Mint]: http://www.linuxmint.com/ [Create an Empty Virtual Machine]: #create-an-empty-virtual-machine-in-vmware [**CentOS-6.5-i386-minimal.iso**]: http://cstech/repo/linux/CentOS/CentOS-6.5-i386-minimal.iso/ [`CentOS-6.5-i386-minimal.iso`]: http://cstech/repo/linux/CentOS/CentOS-6.5-i386-minimal.iso/CentOS-6.5-i386-minimal.iso [`CentOS-6.5-i386-minimal.iso-md5.txt`]: http://cstech/repo/linux/CentOS/CentOS-6.5-i386-minimal.iso/CentOS-6.5-i386-minimal.iso-md5.txt [**HashTab**]: http://www.implbits.com/hashtab.aspx [**Cygwin**]: http://cygwin.com/ [CentOS 6 Welcome]: data/centos6_welcome.jpg "CentOS 6 Welcome" [CentOS 6 Splash Screen]: data/centos6_splash.jpg "CentOS 6 Splash Screen" [password that you can remember]: http://xkcd.com/936/ [CentOS 6 Partitions]: data/centos6_partitions.jpg "CentOS 6 Partitions" [CentOS 6 Install Packages]: data/centos6_install_packages.jpg "CentOS 6 Install Packages" [Network Diagnostics]: 000_network_diagnostics.html [Remote Login]: 110_remote_login.html [Course Linux Server]: 070_course_linux_server.html [Appendix I]: #appendix-i-what-to-do-if-yum-doesnt-work [Optional Sysadmin Shell Aliases]: 350_startup_files.html#optional-sysadmin-shell-aliases [CentOS 6 GRUB Menu]: data/centos6_grub_menu.jpg "CentOS 6 GRUB Menu" [shut down your machine before taking a snapshot]: #problems-with-snapshots-of-running-systems [CentOS 6 Configuration Snapshot]: data/centos6_configsnap.jpg "CentOS 6 Configuration Snapshot" [**Install VMware Tools**]: 000_centos_vmware_tools.html [`screen`]: http://www.rackaid.com/resources/linux-screen-tutorial-and-how-to/ [`tmux`]: http://www.techrepublic.com/blog/linux-and-open-source/is-tmux-the-gnu-screen-killer/ [Plain Text]: 000_centos_install.txt [Pandoc Markdown]: http://johnmacfarlane.net/pandoc/
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