dd copies data at a low level. It is powerful, but it can overwrite disks if the input and output paths are wrong. Create an image of a disk or partition Write an image to a USB drive Always double-check the target device before running dd. A wrong of= value can destroy data.
cron runs commands on a schedule. User cron entries are edited with crontab. Edit the current user crontab Crontab format Run a script every day at 2:30 AM List existing cron jobs Use full paths inside cron jobs because the environment is usually smaller than an interactive shell.
The whatis command shows a short one-line description from the manual page database. It is useful when you know a command name but want a quick reminder of what it does. Examples For more detail, open the full manual page with man.
The renice command changes the nice value of a process that is already running. It can be useful when a process is using too much CPU or when you want to give a task lower priority. Find the process ID Lower priority of a running process A higher nice value means lower scheduling priority. Raising … Read more
GnuPG implements the OpenPGP standard and can be used to encrypt files or messages and to create digital signatures. It is still useful, but many older email-client instructions and key-generation examples are no longer current. Generate a modern key gpg –full-generate-key Choose a modern algorithm offered by your installed GnuPG version and protect the private … Read more
The which command shows the path of the executable that will run when you type a command name. It is useful when multiple versions of a tool may be installed. Basic use If the command is found in your PATH, which prints the full path. If nothing is printed, the command may not be installed … Read more
The nice command starts a program with a modified scheduling priority. It is useful when you want a background task to be less aggressive with CPU usage. Run a command with lower priority Example Higher nice values mean lower priority. To adjust a process that is already running, use renice.
cdecl and c++decl translate complicated C and C++ declarations into English and can also generate declarations from plain-language descriptions. They are useful when pointer, function-pointer, or nested type syntax becomes hard to read. Interactive mode cdecl explain int (*signal(int, int (*)(int)))(int) declare p as pointer to integer quit c++decl uses C++ terminology and syntax where … Read more
A concise cdecl reference for understanding and constructing complex C type declarations.
The install command copies files while setting ownership, permissions and target directories in one step. It is commonly used in build scripts and deployment tasks. Copy a file with permissions Create a directory with permissions For system locations such as /usr/local/bin, you may need appropriate privileges. Always check the target path before copying files.