Linux Runlevels

The term “runlevel” which is frequently use in UNIX based operating system is refers to “Unix System V-style initialization” mode for operation. There are seven runlevels , numbered from zero to six. “s” is used sometimes as a synonym for level 1. Operating system is boot by use only one runlevel, runlevels are not executing sequentially. Runlevels are defining the state

Command whoami

NAME whoami - print effective userid SYNOPSIS whoami [OPTION]... DESCRIPTION Print the user name associated with the current effective user ID.  Same as id -un. Options Description --help display this help and exit --version output version information and

Command who

NAME who - show who is logged on SYNOPSIS who [OPTION]... [ FILE | ARG1 ARG2 ] DESCRIPTION Print information about users who are currently logged in. Options Description -a, --all same as -b -d --login -p -r -t -T -u -b, --boot time of last system boot -d, --dead print dead processes -H, --heading print line of column headings -l, --login print system login processes --lookup attempt to canonicalize hostnames via DNS -m only hostname and user associated with

Command which

NAME which - shows the full path of (shell) commands. SYNOPSIS which [options] [--] programname [...] DESCRIPTION        Which takes one or more arguments. For each of its arguments it prints to stdout the full path of the executables that would have been executed when this argument had been entered at the shell prompt. It does this by searching for an executable or script

Command whereis

NAME whereis - locate the binary, source, and manual page files for a command SYNOPSIS whereis [-bmsu] [-BMS directory...  -f] filename... DESCRIPTION        whereis  locates  source/binary  and manuals sections for specified files.  The supplied names are first stripped of leading pathname components and any (single) trailing extension of the form .ext, for example, .c.  Prefixes of s.  resulting from use of source code control

Command wc

NAME wc - print newline, word, and byte counts for each file SYNOPSIS wc [OPTION]... [FILE]... wc [OPTION]... --files0-from=F DESCRIPTION        Print  newline, word, and byte counts for each FILE, and a total line if more than one FILE is specified.  With no FILE, or when FILE is -, read standard input. Options Description -c, --bytes print the byte counts -m, --chars print the character counts -l, --lines print the newline counts --files0-from=F read input

Command watch

NAME watch - execute a program periodically, showing output fullscreen SYNOPSIS watch [-dhvt] [-n <seconds>] [--differences[=cumulative]] [--help] [--interval=<seconds>] [--no-title] [--version] <command> DESCRIPTION        watch  runs command repeatedly, displaying its output (the first screenfull).  This allows you to watch the program output change over time.  By default, the program is run every 2 seconds; use -n or --interval to specify a different interval.        The -d

Command vmstat

NAME vmstat - Report virtual memory statistics SYNOPSIS vmstat [-a] [-n] [-t] [-S unit] [delay [ count]] vmstat [-s] [-n] [-S unit] vmstat [-m] [-n] [delay [ count]] vmstat [-d] [-n] [delay [ count]] vmstat [-p disk partition] [-n] [delay [ count]] vmstat [-f] vmstat [-V] DESCRIPTION vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity. The  first report produced gives averages since the last reboot.  Additional

Command vdir

NAME vdir - list directory contents SYNOPSIS vdir [OPTION]... [FILE]... DESCRIPTION List information about the FILEs (the current directory by default).  Sort entries alphabetically if none of -cftuvSUX nor --sort. Mandatory arguments to long options are mandatory for short options too. Options Description -a, --all do not ignore entries starting with . -A, --almost-all do not list implied . and .. --author with -l, print the author of each file -b, --escape print octal escapes

Command uudecode

NAME uudecode - decode a binary file SYNOPSIS uudecode [-o outfile][file] DESCRIPTION        The uudecode utility shall read a file, or standard input if no file is specified, that includes data created by the uuencode utility. The uudecode  utility  shall  scan the input file, searching for data compatible with one of the formats specified in uuencode, and attempt to create or overwrite the file