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RE: Interview Questions for a Unix Solaris System Admin

From: Matthew Zito <>
Date: Wed, 16 Jul 2003 11:56:40 -0400
Message-Id: <>

Yeah, well....ummm...yeah, okay - that was dumb of me. Here they are:

  1. What is an inode? Answer: An inode is an on-disk data structure that contains information about a file. Useful things it includes are size, modification time, and number of links that point to it (among other things) Bonus: What is not included in an inode? Answer: The file name. That comes from the referencing directory entry.
  2. What is priority paging and how does it work? Answer (short version): Priority paging is a workaround for an irritating VM problem on Solaris 2.6 (and 7? memory escapes me at the moment) where buffered filesystem data was considered equally valued as application memory, and so large amounts of buffered filesystem i/o could actually cause applications to be swapped out. Priority paging, enabled in the /etc/system file, modifies the paging algorithm to reduce the effects of that. It doesn't come by default in solaris 2.6 - you need to install a later kernel patch for it (105181-21? maybe? bueller?)

3)What does sr stand for in vmstat output? Answer: Scan Rate - how often the kernel is sweeping through memory space looking for pages that can be marked inactive. It is not a problem necessarily, but rather an indication of memory pressure.

4) how would I configure the gigabit ethernet interface to force it to be full duplex?
Answer: ndd /dev/ge and there's like four parameters you have to set, plus turning the autoneg_cap off.

5) How does raid-5 work?
Answer: According to BAARF, poorly.
Answer: dedicated parity disk
Answer: dedicated parity disk w/ synchronized spindles

6) Difference between passwd and shadow files? Answer: the passwd has a "x" where the crypted password hash would be, while the hash goes in the shadow file. That's to prevent brute-force space searches for passwords by non-root users. The side effect, though, is that now applications that authenticate users need to be setuid, which opens up other secuity holes. The moral? You can't win.

7) What's the difference between rdsk and dsk? Answer: rdsk is raw, which has two implications - one, its a character device and two, it bypasses the system buffer cache. Bonus: difference between block and character? Answer: character devices take input one character at a time, while block devices take a quantity of data. The system calls for accessing said data also differ, but its too much to write now.

8) How do journaling filesystems work?
Answer: by creating a journal, or intent log, about metadata changes that are going to occur to the filesystem. When a crash occurs, the journal is replayed.

9) What's the difference between ssh and telnet? Why is one preferable over the other?
Answer: ssh is encrypted, which protects not just against people sniffing your traffic, but it prevents malicious session hijacking as well. There's no justification for telnet anymore - at the point when a cisco router can run ssh, so can your servers.

  1. What's the difference between the e4000 and e4500, 6000 and 6500, etc.? Answer: the backplane (and hence, processor) speed. the eX500 series runs at a 100 MHz on the backplane, while the eX000 runs at 83? (not sure). The one exception is the e6500, which runs at 90 MHz normally due to its increased centerplane length.
  2. What happens on an E6500 when I add boards in the bottom two slots? Answer: the centerplane steps down again from 90 MHz to 83, making it the same speed as an E6000 at that point. The problem is the length of the centerplane and electrical latency....stupid speed of light.
  3. On an Sbus e-class I/O tray, what performance considerations do I have to keep in mind when I'm installing Sbus cards? Answer: even though there are three sbus slots in a Sun I/O tray, there are only two controllers. Slot 0 is its own sbus controller, and then slots 1 and 2 share one. So, distribute your heavy vs. low i/o cards accordingly.
  4. Why is NIS bad? Answer: no encryption, no strong authentication, no non-repudiation - basically completely devoid of any of the major AAA (Authorization, Authentication, and Accounting) principles of security systems.
  5. What's the diff between TCP and UDP? Answer: tcp is connection-oriented, has all sorts of crafty algorithms to improve performance. UDP has none of those things.
  6. How does DNS work? Answer: tree-based directory infrastructure, concepts of recursion and authoritative delegation. Too much to write in this email. Bonus: Is DNS TCP or UDP? Answer: Both. DNS requests and responses smaller than 512 bytes are UDP. If for some reason a request results in a >512 byte response, the server sends back a UDP packet with the TC (truncate) bit sent and the client retries using TCP. Also, zone transfers are always TCP.

Bleh. There. My secrets are revealed. Good thing I don't have to deal with Solaris much anymore.


Matthew Zito
GridApp Systems
Received on Wed Jul 16 2003 - 10:56:40 CDT

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