Commands tagged hex (25)

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Generate a binary file with all ones (0xff) in it
This is similar to how you would generate a file with all zeros $ dd if=/dev/zero of=allzeros bs=1024 count=2k

copy root to new device
Clone a root partition. The reason for double-mounting the root device is to avoid any filesystem overlay issues. This is particularly important for /dev. Also, note the importance of the trailing slashes on the paths when using rsync (search the man page for "slash" for more details). rsync and bash add several subtle nuances to path handling; using trailing slashes will effectively mean "clone this directory", even when run multiple times. For example: run once to get an initial copy, and then run again in single user mode just before rebooting into the new disk. Using file globs (which miss dot-files) or leaving off the trailing slash with rsync (which will create /mnt/target/root) are traps that are easy to fall into.

Print a row of characters across the terminal
shorter than alternative

Sort a character string
Sorts a character string, using common shell commands.

Rename files in batch

Find out what package some command belongs to (on RPM systems)
Replace 'more' command with any command which is in your PATH.

Clean the /boot directory
On Fedora clean the boot directory; erase older kernel

prints line numbers
the sed way to print line numbers

Skip banner on ssh login prompt
This allows you to skip the banner (usually /etc/issue.net) on ssh connections. Useful to avoid banners outputted to your mail by rsync cronjobs.

Find ulimit values of currently running process
When dealing with system resource limits like max number of processes and open files per user, it can be hard to tell exactly what's happening. The /etc/security/limits.conf file defines the ceiling for the values, but not what they currently are, while $ ulimit -a will show you the current values for your shell, and you can set them for new logins in /etc/profile and/or ~/.bashrc with a command like: $ ulimit -S -n 100000 >/dev/null 2>&1 But with the variability in when those files get read (login vs any shell startup, interactive vs non-interactive) it can be difficult to know for sure what values apply to processes that are currently running, like database or app servers. Just find the PID via "ps aux | grep programname", then look at that PID's "limits" file in /proc. Then you'll know for sure what actually applies to that process.


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