banner can be a useful command for setting login and welcome messages (e.g via /etc/profile). $ banner PRODUCTION ###### ###### ####### ###### # # ##### ####### ### ####### # # # # # # # # # # # # # # # # # # ## # # # # # # # # … Continue reading Linux command of the day: banner

I ran into this error when running ec2-upload-bundle:The specified bucket is not S3 v2 safe (see S3 documentation for details)This was due to uppercase letters or underscores. Later I also ran into an issue with periods in bucket names which showed up as this error message:ERROR: Error talking to S3: Server.AccessDenied(403): Access DeniedHere is an … Continue reading The specified bucket is not S3 v2 safe

By default, Bash treats uninitialized variables the same way as Perl -- they are blank strings. If you want them treated more like Python, you can issue the following command in your bash script: set -u You will then start seeing warning messages like the following: ./my_script.sh: line 419: FOO_BAR: unbound variable Note that this … Continue reading Have bash warn you about uninitialized variables with set -u

mkdir -p is a command second only to touch in succinct utility. touch creates a file if it does not exist, or updates its timestamp if it does. It's handy if you want to write to a file without checking for its existence, as otherwise you'd need to determine whether or not append is the … Continue reading mkdir -p is your friend

The startup order of services on Red Hat Enterprise Linux (and very likely other flavours) is determined by the numerical prefix on the symbolic links in /etc/rc3.d/ (for run level 3), /etc/rc5.d/ (for run level 5), and so on. When adding a service (chkconfig --add my_service --level 35), you can specify startup order by including … Continue reading Startup order of services on RHEL or CentOS

The Linux command line can be a bit intimidating at first, but it gets much easier once you learn a few basic building blocks. The power of the command line lies in combining many basic commands in interesting ways. Open up a Linux terminal (or, if you want to follow along on Windows, Cygwin). The … Continue reading Linux Basics: Navigate with ls, cd, and pwd