February 7, 2012 at 15:46Check List for Stupid Things - Limoncelli
Many are familiar with the books of Thomas Limoncelli on system administration, which are very valuable for admin books. On his site, too, a lot of interesting things, among other things, I found this article: “A list of dumb things to check” . In Russian, she, unfortunately, did not google it, he translated it himself. After doping under my conditions, I will use it as part of KMB in my department, and I post the initial translation here.
I didn’t master some points (there wasn’t enough language or technical knowledge), but I think it’s suitable for practical use. Author punctuation partially retained.
The article (and his entire blog) is distributed under CC-BY-NC-SA.
"
You solve the problem for many hours and suddenly realize: “I bet I’m dealing with some kind of stupidity!” Often it is. Therefore, we present ...
Added: 2009-11-25: People refer to this as something funny. Hell, this list is 100% true! All these things happened to me and made me think: “Better I’ll write it all down so that I don’t forget anything!” Even the last point!
1. Make sure CapsLock is turned off. (Same for ScrollLock and NumLock)
2. Type this again (without copy-paste) and see if the result is the same. (helps with typos) (and from the unicode character "whitespace")
3. Copy and paste the variable name (or URL, command, etc.) to make sure it is entered correctly.
4. Do you run the programs that you think? (Maybe you installed them in single-user mode when / opt was not mounted? Can you compare the checksums of the files of this machine and the machine that is working correctly?)
5. Check the file permissions.
6. Is it really that computer that you think?
7. Are you checking from the right machine? Maybe it will be more effective on the other?
8. Does the validation really check what you think? What if you check for known-good and obviously bad systems? Did you get the results you expected?
9. Is it a file, directory, hard link, symbolic link or mount point?
10. Is the file extension correct? Maybe it should be .php, not .html?
11. Is the screen stopped by pressing Ctrl-S? (Press Ctrl-Q to find out)
12. Can you get to the website? Do you work offline?
1. Are both ends of the power / network / video / ... cable connected?
2. Is the cable connected to the correct connector?
3. Have you tried unplugging the cable and plugging it in again to make sure it is ok?
4. To the question "Is it connected?" it’s very simple to answer “Yes.” It is better to ask to turn it off and on again, or check both ends of the power cable, or ask if the power indicator is on, off, or blinking.
5. If you turn on the lamp in this outlet - will it light up?
6. Is it a laptop that runs on battery power? (and, thus, does not allow to notice a problem with the power supply)
7. Is the driver that you install really from your device?
1. Is there an extraneous DHCP server in the network?
2. Is the address pool on the DHCP server exhausted, are there any remaining addresses?
3. Does the VPN connection break at arbitrary points, and does the server receive an ICMP response “host unreachable”? The firewall of the client computer blocks ARP, and after the expiration of the ARP cache storage time (300 seconds), the router cannot send packets to it. (Some manufacturers keep the ARP record of the address all the time while they receive packets from this address (Cisco), but most do not) (I added this because I met this in two places)
1. Is a default gateway specified? Is the network mask set correctly?
2. http://www.psc.edu/~mathis/MTU/index.html : six classes of problems that reduce network performance:
* packet loss, damage, congestion, faulty equipment
* IP routing, high RTT (round trip time )
* packet reordering
* inappropriate buffer space
* inappropriate packet size
* inefficient applications
3. Does anyone else have this IP address? (Disconnect the network cable and ping the address)
4. (problems with firewall rules) Does the problem remain after changing the IP address? Does the problem remain after moving to another subnet? Does the problem remain if you give this IP address to another machine? Does the problem remain if you load another OS (for example, Linux or FreeBSD from a CD-ROM)?
5. Will the same problem arise if an IP address is specified instead of a machine name?
1. Trace from A to B. Then from B to A. Do they match each other?
1. SSH, SCP, L2TP, PPTP
1. Does the program read the last line of the file? Is it being processed correctly?
2. Are there (invisible) Ctrl-Ms at the end of each line of a text file?
3. Does the file end with a line break?
4. If the line ends with the escape character "\", does it really end with it? Is there an invisible space or tab after it? An invisible space or tab can cause a shell error of "unexpected |" ("Unexpected |")!
1. Is DNS configured correctly? An error in the DNS settings hides other problems and looks like a problem whose solution you will look for anywhere except /etc/resolv.conf
2. Check the environment variables.
3. Do you run the copy of the script you are editing?
4. Does the program look for the configuration file in the same place as you? (Maybe the new version is looking for it at /etc/example2/example.conf instead of the old address /etc/example.conf?)
1. Do users really press RETURN when you guess? (Do they click it at all?)
2. Does the user write "/" or "\"?
3. Does the user know what the characters “less” (<) and “more” (>) are?
4. "Do you have permission to crack this password file?" ... "Is it in writing?"
5. Today is the first day of the month? Maybe there was a problem with billing, and something turned off.
6. Accurately measure how often the problem occurs, or after how long it occurs. Mark outages on the timeline. What protocol can they be associated with?
ARP caches are stored for 300 seconds. Routing protocols are usually updated every 5 or 15 minutes. Once I built a schedule of “network pauses” and saw that they happen every 10 minutes, but not only: the router CPU was overloaded with a process that started every 10 minutes AND every time the RIP was updated. Without a schedule, I would only notice a “every 10 minutes” component.
Have you forgotten to check this list?
Tom Limoncelli
»
Original .
I didn’t master some points (there wasn’t enough language or technical knowledge), but I think it’s suitable for practical use. Author punctuation partially retained.
The article (and his entire blog) is distributed under CC-BY-NC-SA.
"
You solve the problem for many hours and suddenly realize: “I bet I’m dealing with some kind of stupidity!” Often it is. Therefore, we present ...
check list of stupid things
Added: 2009-11-25: People refer to this as something funny. Hell, this list is 100% true! All these things happened to me and made me think: “Better I’ll write it all down so that I don’t forget anything!” Even the last point!
Level 0 - Human
1. Make sure CapsLock is turned off. (Same for ScrollLock and NumLock)
2. Type this again (without copy-paste) and see if the result is the same. (helps with typos) (and from the unicode character "whitespace")
3. Copy and paste the variable name (or URL, command, etc.) to make sure it is entered correctly.
4. Do you run the programs that you think? (Maybe you installed them in single-user mode when / opt was not mounted? Can you compare the checksums of the files of this machine and the machine that is working correctly?)
5. Check the file permissions.
6. Is it really that computer that you think?
7. Are you checking from the right machine? Maybe it will be more effective on the other?
8. Does the validation really check what you think? What if you check for known-good and obviously bad systems? Did you get the results you expected?
9. Is it a file, directory, hard link, symbolic link or mount point?
10. Is the file extension correct? Maybe it should be .php, not .html?
11. Is the screen stopped by pressing Ctrl-S? (Press Ctrl-Q to find out)
12. Can you get to the website? Do you work offline?
Level 1 - Physical
1. Are both ends of the power / network / video / ... cable connected?
2. Is the cable connected to the correct connector?
3. Have you tried unplugging the cable and plugging it in again to make sure it is ok?
4. To the question "Is it connected?" it’s very simple to answer “Yes.” It is better to ask to turn it off and on again, or check both ends of the power cable, or ask if the power indicator is on, off, or blinking.
5. If you turn on the lamp in this outlet - will it light up?
6. Is it a laptop that runs on battery power? (and, thus, does not allow to notice a problem with the power supply)
7. Is the driver that you install really from your device?
Level 2 - Channel
1. Is there an extraneous DHCP server in the network?
2. Is the address pool on the DHCP server exhausted, are there any remaining addresses?
3. Does the VPN connection break at arbitrary points, and does the server receive an ICMP response “host unreachable”? The firewall of the client computer blocks ARP, and after the expiration of the ARP cache storage time (300 seconds), the router cannot send packets to it. (Some manufacturers keep the ARP record of the address all the time while they receive packets from this address (Cisco), but most do not) (I added this because I met this in two places)
Level 3 - Network
1. Is a default gateway specified? Is the network mask set correctly?
2. http://www.psc.edu/~mathis/MTU/index.html : six classes of problems that reduce network performance:
* packet loss, damage, congestion, faulty equipment
* IP routing, high RTT (round trip time )
* packet reordering
* inappropriate buffer space
* inappropriate packet size
* inefficient applications
3. Does anyone else have this IP address? (Disconnect the network cable and ping the address)
4. (problems with firewall rules) Does the problem remain after changing the IP address? Does the problem remain after moving to another subnet? Does the problem remain if you give this IP address to another machine? Does the problem remain if you load another OS (for example, Linux or FreeBSD from a CD-ROM)?
5. Will the same problem arise if an IP address is specified instead of a machine name?
Level 4 - Transport
1. Trace from A to B. Then from B to A. Do they match each other?
Level 5 - Session
1. SSH, SCP, L2TP, PPTP
Level 6 - Executive
1. Does the program read the last line of the file? Is it being processed correctly?
2. Are there (invisible) Ctrl-Ms at the end of each line of a text file?
3. Does the file end with a line break?
4. If the line ends with the escape character "\", does it really end with it? Is there an invisible space or tab after it? An invisible space or tab can cause a shell error of "unexpected |" ("Unexpected |")!
Level 7 - Applied
1. Is DNS configured correctly? An error in the DNS settings hides other problems and looks like a problem whose solution you will look for anywhere except /etc/resolv.conf
2. Check the environment variables.
3. Do you run the copy of the script you are editing?
4. Does the program look for the configuration file in the same place as you? (Maybe the new version is looking for it at /etc/example2/example.conf instead of the old address /etc/example.conf?)
Level 8 - User / Political
1. Do users really press RETURN when you guess? (Do they click it at all?)
2. Does the user write "/" or "\"?
3. Does the user know what the characters “less” (<) and “more” (>) are?
4. "Do you have permission to crack this password file?" ... "Is it in writing?"
5. Today is the first day of the month? Maybe there was a problem with billing, and something turned off.
6. Accurately measure how often the problem occurs, or after how long it occurs. Mark outages on the timeline. What protocol can they be associated with?
ARP caches are stored for 300 seconds. Routing protocols are usually updated every 5 or 15 minutes. Once I built a schedule of “network pauses” and saw that they happen every 10 minutes, but not only: the router CPU was overloaded with a process that started every 10 minutes AND every time the RIP was updated. Without a schedule, I would only notice a “every 10 minutes” component.
If all else fails
Have you forgotten to check this list?
Tom Limoncelli
»
Original .