Unix users write, edit, list, and remove cron jobs using the `crontab` command. `crontab -e` takes users into their default editor to edit their crontab entries. `crontab -l` lists their crontab. `crontab -r` removes their crontab. crontab Security If the cron.allow file exists, then the user must be listed in that file in order to …
One of the best methods to capture a Unix terminal session is to use the `script` command. In this example we start a script session, run a couple of commands, and then use the `exit` command to stop capturing the terminal session: $ script Script started, output file is typescript $ pwd /home/will $ ps …
A computer process is a computer program that is executing and has a unique process identification or PID. On the Unix Operating System (OS), a process may be running in the background, foreground, or be in a suspended state. On Unix, the OS shell will not return the prompt to the end-user until the current …
Unix file permissions are based upon an octal code. Unix file permissions are stored in a ten character array. The first character of the file permissions stores the file type. The standard file types are: Character Meaning – Plain file d Directory c Character device b Block device l Symbolic link s Socket = or …
One way that a small business that requires a file server can save thousands of dollars per year is to set up a Linux file server. Linux is an open source software platform that, in many ways, is just as good as or better than other types of platforms including Microsoft and Sun. Small businesses …
Tar refers to a tape archiving file format and the program that creates them. Tar stands for tape archive. It combines multiple files together so that they can be used for programs, applications, and critical system files. While Tar does not directly install files to a user’s hard drive, it is responsible for compiling the …
A signal is a message that can be sent to a running process. Programs, users, or administrators can initiate signals. For example, the proper method of telling the Internet Daemon (inetd) to re-read its configuration file is to send it a SIGHUP signal. For example, if the current process ID (PID) of inetd is 4140, …
Top is a small, but powerful program on both Unix and Linux systems. Its purpose is to allow users to monitor processes on their system. It has two main sections. The first displays general information such as the load averages, number of running and sleeping tasks, and overall CPU and memory usage. The second main …
umask is a Unix shell built-in command that automatically sets file permissions on newly created files. The umask command can be confusing to use because it does work as a mask. In other words, the user sets the permissions that he/she does not want in the umask. To calculate permissions that will result from specific …
The total number of Unix commands is immense. No normal user or system administrator would ever need to know them all. The Unix commands available to you will vary based upon several factors: The version of Unix you are using (FreeBSD, Linux, Solaris, AIX, HP-UX, OpenBSD, etc…) The Unix shell you are using (sh, csh, …