Best of Technical Support

Our experts answer your technical questions.
Where's /dev/sdc?

I have two IDE devices, a 40GB WD HDD and a CD-RW drive. I also have a SIIG SCSI card. I believe that Linux is recognizing my SCSI card, but for some reason I cannot get access to my SCSI drives. When I try /dev/MAKEDEV sdc[0,1, ..., n], it tells me:

don't know how to make sdc[n].

My SCSI hdd is set to id 3. My SCSI CD-ROM is set to id 5 and my SCSI card is defaulted to id 7. Everything is terminated properly. What's the deal?

—Derrick Blackwell, db101055@hotmail.com

You seem to expect the HD with SCSI address 3 to be /dev/sdc. Linux doesn't work like that: the lowest-addressed SCSI HD is always /dev/sda, regardless of its SCSI address. The next-higher-addressed SCSI HD is always /dev/sdb, and so on. Your SCSI CD will be /dev/scd0 or /dev/sr0—both names work equally well.

—Scott Maxwell, maxwell@ScottMaxwell.org

What the fsck? The Superblock Could Not Be Read

When I e2fsck /dev/hda, I get the following message:

The superblock could not be read or does not describe
a correct ext2 filesystem. If the device is valid
and it really contains an ext2 filesystem (and not
swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an
alternate superblock: e2fsck -b 8193 <device>

When I do as it says (<device> = dev/hda), I get the same message back. This is is the fourth time it has happened. The other times I just reloaded Red Hat, as I had not lost anything significant. This time I prefer to not lose programs I had working.

—Bob Wooden, bwooden@computelnet.com

/dev/hda is a drive. While it is possible to install a filesystem on a drive, this is most likely not the way it was installed. You should do a fdisk -l /dev/hda, which will show you all the partitions installed on the hda drive. Most likely, your partition is /dev/hda1 unless you are dual booting.

—Christopher Wingert, cwingert@qualcomm.com

/proc/kcore: 0wn3d!

I have two servers running Red Hat 7.1. I run Tripwire on both servers. Tripwire has twice reported that the file /proc/kcore has changed. Is this something that happens? No reboots between the occasions.

The file /lib/libc-2.2.2.so did change checksum, but nothing else was changed; dates, inode, etc., were the same. rpm -V glibc also revealed that the file MD5 checksum was altered. Since I am running a public web server on this machine, I reinstalled the glibc package. Then Tripwire complained about the dates and inodes; this is natural when you have reinstalled a package. I believe I have a well-setup firewall. How can the checksum of libc change? Why does the checksum of kcore change?

—Magnus Sundberg, Magnus.Sundberg@dican.se

I don't know why libc changed, but I know why /proc/kcore changed: /proc/kcore is a pseudo-file representing the system's physical memory. It's only natural that the contents of physical memory would vary with time. If it didn't, your system would be a lot less useful. So don't worry about that one.

—Scott Maxwell, maxwell@ScottMaxwell.org

If I Could Walk That Way, I Wouldn't Need Aftershave!

I am having trouble using two NICs in my Red Hat 7.2 (2.4.3-12) machines. Both NICs are recognized, and I can configure them. But I have two T1s from different providers, thus on different IP networks. I want to multihome these machines, but I cannot figure out how to add a default route for each NIC.

—Mike Kercher, mike@CamaroSS.net

You cannot add two default routes. You have to tell Linux which traffic should go to which network. Sounds like what you are trying to do is load balancing on the two T1s (or possibly redundancy). Check out the EQL or Bonding driver. You also could route via BGP. Check out the Advanced Routing HOWTO at www.linuxdoc.org/HOWTO/Adv-Routing-HOWTO.html.

—Christopher Wingert, cwingert@qualcomm.com

Yes, Sir, We Have Aftershave—Walk This Way Please

I have about 300 Linux servers and the floor space in the data center is at a premium. I need to access the servers as console for administration purposes, but they do not have monitors. Is there some way I could get a serial terminal connected as a console?

—Karthik, nkk@hotmail.com

Check out the Serial Console HOWTO at www.linuxdoc.org/HOWTO/Remote-Serial-Console-HOWTO.

—Christopher Wingert, cwingert@qualcomm.com

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