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Lack of testing complex, potentially destructive, commands before execution of production box

News Enterprise Unix System Administration Recommended Links Simple Unix Backup Tools Unix rm command Unix mv command
Absence of backup Rush/absence of testing Creative uses of rm Abuse of privileges LVM and disk related mishaps Working on the wrong computer
Safe-rm Typical Errors In Using Find Tips Unix History Humor Etc

Amount of testing of complex commands, especially those that involve recursive operations should generally be proportional to potential damage.

This is often not the case. One common mishap is running as root complex command like  find  ... -exec rm {} \; without any testing or even rereading the command several times before hitting Enter.   Never ever assume that some prepackaged script that you are running does anything right. Beware anything recursive when logged in as root!
 

Such errors are often made under time pressure. As for find example above instead of rm other commands can be equally destructive, for example chown or, especially, chmod. 

  1. Running complex rm command without testing it using ls . You should always use ls -Rl command to test complex rm  -R  commands (  -R, --recursive means process  subdirectories recursively).
     
  2. Mistyping complex path or file name in rm commands. It's always better to use copy and paste operation for directories and files used in rm command as it helps to avoid various typos. If you do recursive deletion is is useful to have a "rty run" using las of find to see the files.

    Here are to example of typos:

    rm -rf /tmp/foo/bar/ *

    instead of

    rm -rf /tmp/foo/bar/*

    ===

    rm -r /etc

    instead of

    rm -r etc

    This actually is an interesting type of error because /etc is typed daily so often that it kind of ingrained in sysadmin head and can be typed subconsciously instead of etc

    In some situation results can be devastating. For example, in the example above you would erase all your files and subdirectories in the /etc directory. Modern flavors of Unix usually prevent erasing / but not /etc.

    Again, it's much safer to list the directory and copy it using cut and paste.

    You can also hit Enter by mistake before finishing typing the line containing rm command. 

Here is a couple of examples:

From: mfraioli@grebyn.com (Marc Fraioli)

Organization: Grebyn Timesharing

Well, here's a good one for you:

I was happily churning along developing something on a Sun workstation, and was getting a number of annoying permission denieds from trying to write into a directory heirarchy that I didn't own. 

Getting tired of that, I decided to set the permissions on that subtree to 777 while I was working, so I wouldn't have to worry about it.  Someone had recently told me that rather than using plain "su", it was good to use "su -", but the implications had not yet sunk in.  (You can probably see where this is going already, but I'll go to the bitter end.) 

Anyway, I cd'd to where I wanted to be, the top of my subtree, and did su -.  Then I did chmod -R 777.  I then started to wonder why it was taking so damn long when there were only about 45 files in 20 directories under where I (thought) I was. 

Well, needless to say, su - simulates a real login, and had put me into root's home directory, /, so I was proceeding to set file permissions for the whole system to wide open. I aborted it before it finished, realizing that something was wrong, but this took quite a while to straighten out.

Marc Fraioli

Oh you bastards. I was hoping that a thread like this would never appear, because if it did, I knew I would have to confess. Oh well...

About a year back, I was looking through /etc and found that a few system files had world write permission.  Gasping with horror, I went to put it right with something like

dipshit# chmod -r 664 /etc/*

(I know, I know, goddamnit!.. now)

Everything was OK for about two to three weeks, then the machine went down for some reason (other than the obvious).  Well, I expect that you can imagine the result.  The booting procedure was unable to run fsck, so barfed and mounted the file systems read-only, and bunged me into single-user mode. Dumb expression..gradual realisation..cold sweat.

Of course, now I can't do a frigging chmod +x on anything because it's all read-only. In fact I can't run anything that isn't part of sh.

Wedgerama. Hysteria time. Consider reformatting disks. All sorts of crap ideas. Headless chicken scene. Confession.

"You did WHAT??!!"

Much forehead slapping, solemn oaths and floor pacing.

Luckily, we have a local MegaUnixGenius who, having sat puzzled for an hour or more, decided to boot from a cdrom and take things from there. He fixed it.

My boss, totally amazed at the fix I'd got the system into, luckilysaw the funny side of it.  I didn't.  Even though at that stage, I didn't know much about unix/suns/booting/admin, I did actually know enough to NOT use a command like the one above. Don't ask. Must be the drugs.

BTW, if my future employer _is_ reading this (like they say he/she might), then I have certainly learned tonnes of stuff in the last year, especially having had to set up a complete Sun system, fix local problems, etc :-)

Anyone else got a tale of SGS (Spontaneous Gross Stupidity) ?

-dave "I'm much better now, honest.. no, really.. hey what's this button doooooooooOOOOOO..."

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