set -e causes the shell to exit if any subcommand or pipeline returns a non-zero status. The answer the interviewer was probably looking for is: It would be dangerous to use “set -e” when creating init.d scripts: From http://www.debian.org/doc/debian-policy/ch-opersys.html 9.3.2 — Be careful of using set -e in init.d scripts. Writing correct init.d scripts requires … Read more
Virtual memory isn’t even necessarily memory. For example, if a process memory-maps a large file, the file is actually stored on disk, but it still takes up “address space” in the process. Address space (ie. virtual memory in the process list) doesn’t cost anything; it’s not real. What’s real is the RSS (RES) column, which … Read more
Check for files on located under mount points. Frequently if you mount a directory (say a sambafs) onto a filesystem that already had a file or directories under it, you lose the ability to see those files, but they’re still consuming space on the underlying disk. I’ve had file copies while in single user mode … Read more
You can turn off history substitution using set +H.
You can press ctrl-z to interrupt the process and then run bg to make it run in the background. You can show a numbered list all processes backgrounded in this manner with jobs. Then you can run disown %1 (replace 1 with the process number output by jobs) to detach the process from the terminal. … Read more
Bash has a “loadable” sleep which supports fractional seconds, and eliminates overheads of an external command: $ cd bash-3.2.48/examples/loadables $ make sleep && mv sleep sleep.so $ enable -f sleep.so sleep Then: $ which sleep /usr/bin/sleep $ builtin sleep sleep: usage: sleep seconds[.fraction] $ time (for f in `seq 1 10`; do builtin sleep 0.1; … Read more
For system-wide use, OpenSSL should provide you /etc/ssl/certs and /etc/ssl/private. The latter of which will be restricted 700 to root:root. If you have an application that doesn’t perform initial privilege separation from root, then it might suit you to locate them somewhere local to the application with the relevantly restricted ownership and permissions.
Just use a command like: ethtool eth0 to get the needed info. Ex: $ sudo ethtool eth0 | grep Speed Speed: 1000Mb/s
One of the tricks I follow is to put # in the beginning while using the rm command. root@localhost:~# #rm -rf / This prevents accidental execution of rm on the wrong file/directory. Once verified, remove # from the beginning. This trick works, because in Bash a word beginning with # causes that word and all … Read more
The sites-* folders are managed by nginx_ensite and nginx_dissite. For Apache httpd users who find this with a search, the equivalents is a2ensite/a2dissite. The sites-available folder is for storing all of your vhost configurations, whether or not they’re currently enabled. The sites-enabled folder contains symlinks to files in the sites-available folder. This allows you to … Read more