Skip to main content

Setting Up Swap Space


                                 Normally, there are only two steps to setting up swap space,creating the partition and adding it to /etc/fstab. A typical fstab entry for a swap partition at /dev/hda6 would look like this:
/dev/hda6
swap
swap
defaults
0
0

The next time you reboot, the initialization scripts will activate it automatically and there's nothing more to be done.

However, if you want to make use of it right away, you'll need to activate it maually. As root, type:
mkswap -f /dev/hda6
swapon /dev/hda6
Swap Files
There might be times when you've run out of swap space and it is not practical to repartition a drive or add a new one. In this case, you can use a regular file in an ordinary partition. All you have to do is create a file of the size you want

dd if=/dev/zero of=/var/my_swap bs=1024 count=131072
and activate it
mkswap -f /var/my_swap
swapon /var/my_swap

This invocation creates a file called
my_swap in /var. It is 128 Mb long (128 x 1024 = 131072). Initially, it is filled with zeros. However, mkswap marks it as swap space and swapon tells the kernel to start using it as swap space. When you are done with it,
swapoff /var/my_swap
rm /var/my_swap
Multiple Swap Areas
More than one swap partition can be used on the same system. Consider an example fstab where there is a single swap partition:
/dev/hda5
/
ext3
defaults
1
1
/dev/hda1
/boot
ext2
defaults
1
2
none
/dev/pts
devpts
gid=5,mode=620
0
0
none
/proc
proc
defaults
0
0
/dev/hda7
/usr
ext3
defaults
1
2
/dev/hda6
swap
swap
defaults
0
0


Imagine replacing the entry for the swap partition with these three lines:
/dev/hda6
none
swap
sw,pri=3
0
0
/dev/hdb2
none
swap
sw,pri=2
0
0
/dev/hdc2
none
swap
sw,pri=1
0
0

This configuration would cause the kernel to use /dev/hda6 first. it has the highest priority assigned to it (pri=3). The maximum priority can be 32767 and the lowest 0. If that space were to max out, the kernel would start using /dev/hdb2, and on to /dev/hdc2 after that. Why such a configuration? Imagine that the newest (fastest) drives are given the highest priority. This will minimize speed loss as swap space usage grows.

It is possible to write to all three simulataneously. If each has the same priority, the kernel will write to them much like a RAID, with commensurate speed increases.
/dev/hda6
none
swap
sw,pri=3
0
0
/dev/hdb2
none
swap
sw,pri=3
0
0
/dev/hdc2
none
swap
sw,pri=3
0
0

Notice that these three partitions are on separate drives, which is ideal in terms of speed enhancement.

Popular posts from this blog

HOW TO EDIT THE BCD REGISTRY FILE

The BCD registry file controls which operating system installation starts and how long the boot manager waits before starting Windows. Basically, it’s like the Boot.ini file in earlier versions of Windows. If you need to edit it, the easiest way is to use the Startup And Recovery tool from within Vista. Just follow these steps: 1. Click Start. Right-click Computer, and then click Properties. 2. Click Advanced System Settings. 3. On the Advanced tab, under Startup and Recovery, click Settings. 4. Click the Default Operating System list, and edit other startup settings. Then, click OK. Same as Windows XP, right? But you’re probably not here because you couldn’t find that dialog box. You’re probably here because Windows Vista won’t start. In that case, you shouldn’t even worry about editing the BCD. Just run Startup Repair, and let the tool do what it’s supposed to. If you’re an advanced user, like an IT guy, you might want to edit the BCD file yourself. You can do this

DNS Scavenging.

                        DNS Scavenging is a great answer to a problem that has been nagging everyone since RFC 2136 came out way back in 1997.  Despite many clever methods of ensuring that clients and DHCP servers that perform dynamic updates clean up after themselves sometimes DNS can get messy.  Remember that old test server that you built two years ago that caught fire before it could be used?  Probably not.  DNS still remembers it though.  There are two big issues with DNS scavenging that seem to come up a lot: "I'm hitting this 'scavenge now' button like a snare drum and nothing is happening.  Why?" or "I woke up this morning, my DNS zones are nearly empty and Active Directory is sitting in a corner rocking back and forth crying.  What happened?" This post should help us figure out when the first issue will happen and completely avoid the second.  We'll go through how scavenging is setup then I'll give you my best practices.  Scavenging s

AD LDS – Syncronizing AD LDS with Active Directory

First, we will install the AD LDS Instance: 1. Create and AD LDS instance by clicking Start -> Administrative Tools -> Active Directory Lightweight Directory Services Setup Wizard. The Setup Wizard appears. 2. Click Next . The Setup Options dialog box appears. For the sake of this guide, a unique instance will be the primary focus. I will have a separate post regarding AD LDS replication at some point in the near future. 3. Select A unique instance . 4. Click Next and the Instance Name dialog box appears. The instance name will help you identify and differentiate it from other instances that you may have installed on the same end point. The instance name will be listed in the data directory for the instance as well as in the Add or Remove Programs snap-in. 5. Enter a unique instance name, for example IDG. 6. Click Next to display the Ports configuration dialog box. 7. Leave ports at their default values unless you have conflicts with the default values. 8. Click N