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230 Cards in this Set
- Front
- Back
difference between soft and hard links
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command: &
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Run the specified program in the background.
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command: ^z
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Suspend the current foreground process.
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command: bg
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put specified process in the background
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command: fg
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put specified process in the foreground
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fuser
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Display the PID of any process using a specified file.
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command: fuser
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identify processes using files or sockets
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command: jobs
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show list of background processes
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kill
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Stop the execution of a process
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killall
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kill all processes executing a specified command.
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nice
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Change the priority of a process.
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command: nohup
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no hangup -- Run a command immune to hangups.
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command: pidof
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locate and print the process id of the specified program.
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command: ps
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get process status information.
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command: pstree
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display the family tree of running processes.
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command: renice
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Change the id of a running process.
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command: top
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Display Linux tasks .... and their resource use.
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signal for: hang up
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(1) SIGHUP
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signal for: Interrupt from keyboard
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(2) SIGINT (default action:terminate)
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signal for: Quit from keyboard
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(3) SIGQUIT (default action is: terminate and do CORE dump)
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signal for: Illegal Instruction
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(4) SIGILL (default action is: terminate and do CORE dump)
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signal for: Abort signal from abort(3)
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(6) SIGABRT (default action is: terminate and do CORE dump)
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signal for: Floating point exception
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(8) SIGFPE (default action is: terminate and do CORE dump)
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signal for: Kill signal
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(9) SIGKILL (default action: term)
NOTE: SIGKILL cannot be caught, blocked, or trapped |
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signal for: Invalid memory reference
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(11) SIGSEGV (default action is: terminate and do CORE dump)
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signal for: Broken pipe: write to pipe with no readers
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(13) SIGPIPE (default action is: Terminate)
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signal for: Timer signal from alarm(2)
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(14) SIGALRM (default action is: Terminate)
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signal for: Termination signal
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(15) SIGTERM (default action is: Terminate)
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signal for: User-defined signal 1
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(30,10,16) SIGUSR1 (default action is: Terminate)
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signal for: User-defined signal 2
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SIGUSR2 31,12,17 (default action is: Terminate)
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signal for: Child stopped or terminated
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(20,17,18) SIGCHLD (default action is IGNore)
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signal for: Continue if stopped
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(19,18,25) SIGCONT (default action is: CONTinue process if stopped)
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signal for: Stop process
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(17,19,23) SIGSTOP default action:stop)
NOTE: SIGKILL cannot be caught, blocked, or trapped |
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signal for: Stop typed at tty
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(18,20,24) SIGTSTP (default action is: stop)
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signal for: tty input for background process
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(21,21,26) SIGTTIN (default action is: stop)
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signal for: tty output for background process
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(22,22,27) SIGTTOU (default action is: stop)
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signal for: Pollable event (Sys V).
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SIGPOLL (default action: Terminate)
Synonym of SIGIO |
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signal for: Profiling timer expired
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(27,27,29) SIGPROF (default action is: Terminate)
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signal for: Bad argument to routine (SVr4)
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(12,-,12) SIGSYS (default action is: Terminate and dump CORE)
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signal for: Trace/breakpoint trap
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(5) SIGTRAP (default action is: Core)
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Signal for: Urgent condition on socket (4.2BSD)
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(16,23,21) SIGURG (default action: Ignore)
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TRAP syntax?
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trap [COMMANDS] [SIGNALS]
example: trap "echo VARIABLE used" DEBUG |
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redirection: script
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Save the activity on your screen to a file.
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redirection: tee
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...copy to stdin to file and screen
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redirection: xargs
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Read multiple arguments from standard input and use them as arguments to some specified command.
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redirection: 2>
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redirect standard-error as specified
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command:
make prompt show current working directory (pwd) |
export PS1='$PWD> '
NOTE: to make it permanent, add to ~/.bashrc |
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command (users): change information displayed by finger
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chfn
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command (users): change user information in bulk
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chpasswd
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command (users): display information about a user
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finger
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command (users): modify information in the system group files
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groupmod
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commands (user): check system group files for validity
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grpck
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commands (user): display group information for a user
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groups
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commands (user): display information about a user
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id
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commands (user): change user password
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passwd
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commands (user): check system password for validity
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pwck
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commands (user): change to a new user id.
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su
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commands (user): add a new user
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useradd
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commands (user): delete a user
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userdel
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commands (user): modify user information
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usermod
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commands (user): display a list of current users
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users OR who
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commands (user): Secure group information
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/etc/gshadow
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commands: check paths for portability and validity?
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pathchk
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commands: Follow a path to the end, if it has one?
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namei
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commands: take a full path...and display all but the last element
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dirname
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commands: take a full path...and display only the last element
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basename
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commands: Display your current environment variables and their values with the command.
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env
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files: executed when starting a bash subshell
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~/.bashrc
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files: executed at login time
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~/.bash_profile
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files: system-wide profile
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/etc/profile
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files: Synonym for bash_profile
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~/.bash_login
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files: executed when a bash shell exits.
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~/.bash_logout
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INVOKING BASH: don't read the "~/.bashrc" initialization file in an interactive shell.
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-norc
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INVOKING BASH: Execute commands from the specified file rather than ~/.bashrc in an interactive shell.
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-rcfile FILENAME
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INVOKING BASH: Don't load the system-wide startup file /etc/profile OR any of the personal initialization files (~/.bash_profile, ~/.bash_login, ~/.profile).
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-noprofile
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INVOKING BASH: display version information
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-version
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INVOKING BASH: Make this shell act as if it were directly invoked from login.
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-login
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INVOKING BASH: do not perform curly brace expansion.
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-nobraceexpansion
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INVOKING BASH: do not use the GNU Readline library to read interactive command lines.
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-nolineediting
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INVOKING BASH: force bash to conform to the Posiz 1003.2 standard
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-posix
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INVOKING BASH: read and execute commands from STRING after processing the options and then exit.
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-c STRING
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INVOKING BASH: force the shell to run interactively.
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-i
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STEPS: Interactive bash...at login
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1. If /etc/profile exists, then source it.
2. If ~/.bash_profile exists, then source it, else if ~/.bash_login exists then source it, else if ~/.profile exists then source it. |
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STEPS: Interactive bash...at logout
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If ~/.bash_logout exists,
source it. |
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STEPS: NON-login Interactive bash at Startup Time.
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If ~/.bashrc exists,
then source it. |
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STEPS: NON-interactive Shells at Startup Time.
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If the environment variable ENV is non-null......expand the variable and source the file named by the value.
If bash is not started in Posix mode.....it looks for BASH_ENV before ENV. So, typically, your ~/.bash_profile contains the following line: if [ -f ~/.bashrc ]; then source ~/.bashrc; fi |
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alias syntax
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alias [-p] [name[=value] ... ]
note: -p option prints the list of aliases (same as alias with no argument) |
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command: remove an alias
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unalias
note: -a would remove all aliases |
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history shortcut: move up
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arrow up
or <Ctrl>-P |
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history shortcut: move down
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arrow down
or <CTRL>-n |
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history shortcut: move to the first line in history.
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<Meta>-<
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history shortcut: move to the end of input history.
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<Meta>->
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HISTORY SHORTCUT: search backward starting at the current line and moving "up" through the history as necessary.
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<Ctrl>-r
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HISTORY SHORTCUT: search forward starting at the current line and moving "down" through the history as necessary.
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<Ctrl>-s
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HISTORY SHORTCUT: search backward starting at the current line and moving "up" through the history as necessary....using a non-incremental search for a string supplied by the user.
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<Meta>-p
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HISTORY SHORTCUT: search forward starting at th ecurrent line and moving "down" through history as necessary .... using non-incremental search for a string supplied by the user.
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<Meta-n
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HISTORY SHORTCUT: yank nth argument of previous command.
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<Meta>-Ctrl>-y
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HISTORY SHORTCUT: Insert last argument to the previous command.
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<Meta>-. , M-_
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HISTORY SHORTCUT: start a history substitution, except when followed by a space, tab, the end of the line, = or (
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! (bang)
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HISTORY SHORTCUT: refer to the previous command. This the synonym for !-1
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!! (bang bang)
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HISTORY SHORTCUT: refer to command line N.
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!n (bang number)
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HISTORY SHORTCUT: refer to the command N lines back
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!-n
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HISTORY SHORTCUT: refer to the most recent command starting with STRING
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!string
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HISTORY SHORTCUT: refer to the most recent command containing STRING
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!?string[`?]
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HISTORY SHORTCUT: the entire command line typed so far.
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!# (bang sharp)
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HISTORY SHORTCUT:
quick substitution. Repeat the last command, replacing STRING1 with STRING2. Equivalent to "!!:s/string1/string2". |
^string1^string2^
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HISTORY SHORTCUT:
write out the current history to the history file. |
history -w
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HISTORY SHORTCUT:
read the current history file and make its contents the history list. |
history -r
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HISTORY SHORTCUT:
append the new history lines. |
history -a
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HISTORY SHORTCUT:
read the history lines not already read from the history file into the current list. |
history -n
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COMMAND COMPLETION:
attempt to do completion on the text before the cursor. |
<Tab>
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COMMAND COMPLETION:
list the possible completions of the text before the cursor. |
<Meta>-?
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COMMAND COMPLETION:
read in the contents of your init file and incorporate any bindings or variable assignments found there. |
<ctrl>-x, <ctrl>-r
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COMMAND COMPLETION:
abort the current editing command and ring the terminal's bell (subject to the setting of "bell-style" |
<ctrl>-g
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COMMAND COMPLETION:
make the next character that you type metafied. |
<Esc>
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COMMAND COMPLETION:
incremental undo, separately remembered for each line. |
<Ctrl>-_, <Ctrl>-x, <Ctrl>-u
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COMMAND COMPLETION:
Undo all changes made to this line. |
<Meta>-r
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Command Line Editing:
move back one character |
<ctrl>-b
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Command Line Editing:
move forward one character |
<ctrl>-f
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Command Line Editing:
delete the character to the left of the cursor |
<del> , <backspace>
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Command Line Editing:
delete the character underneath the cursor |
<Ctrl>-d
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Command Line Editing:
undo the last thing that you did. |
<Ctrl>-u
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Command Line Editing:
move to the start of the line |
<Ctrl>-a
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Command Line Editing:
move to the end of the line. |
<Ctrl>-e
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Command Line Editing:
move forward a word.<Anchor2> |
<Meta>-f
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Command Line Editing:
move backward a word. |
<Meta>-b
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Command Line Editing:
clear the screen, reprinting the current line at the top. |
<Ctrl>-I
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Command Line Editing:
Kill the text from the current cursor position to the end of the line. |
<ctrl>-k
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Command Line Editing:
Kill from the cursor to the end of the current word, or, if between words, to the end of the next word. |
<Meta>-d
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Command Line Editing:
Kill from the cursor the start of the previous word, or, if between words, to the start of the previous word |
<Meta>-DEL
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Command Line Editing:
kill from the cursor to the previous whitespace. This is different from M-DEL because the word boundaries differ. |
<Ctrl>-w
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Command Line Editing:
Yank the most recently killed taext back into the buffer at the cursor |
<Ctrl>-y
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Command Line Editing:
Rotate the kill-ring, and yank the new top. You can do this only if the prior command is yank or yank-pop. |
<Meta>-y
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Command Line Editing:
Delete the character under the cursor. |
<Ctrl>-d
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Command Line Editing:
Add the next character that you type to the line vertabim. |
<Ctrl>-q, C-w
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Command Line Editing:
Insert a tab character. |
<Meta>-<Tab>
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Command Line Editing:
Drag the chaaracter before the cursor forward over the character at the cursor....moving the cursor forward as well. |
<Ctrl>-t
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Command Line Editing:
Drag the word behind the cursor, past the word in front of the cursor....moving the cursor over that word as well. |
<Meta>-t
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Command Line Editing:
Uppercase the current (or following) word. |
<Meta>-u
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Command Line Editing:
Lowercase the current (or following) word. |
<Meta>-I
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Command Line Editing:
Capitalize the current (or following) word. |
<Meta>-c
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SHELL PROMPT (special characters):
The time, in HH:MM:SS format |
\t
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SHELL PROMPT (special characters):
The time in 12-hour HH:MM:SS format. |
\T
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SHELL PROMPT (special characters):
The time in 12-hour am/pm format. |
\@
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SHELL PROMPT (special characters):
The date, in "Weekday Month Date" format (e.g., "Tue May 26"). |
\d
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SHELL PROMPT (special characters):
ASCII escape character. |
\e
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SHELL PROMPT (special characters):
newline |
\n
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SHELL PROMPT (special characters):
The name of the shell. |
\s
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SHELL PROMPT (special characters):
The current working directory. |
\w
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SHELL PROMPT (special characters):
The basename of $PWD. |
\W
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SHELL PROMPT (special characters):
Your username. |
\u
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SHELL PROMPT (special characters):
hostname |
\h
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SHELL PROMPT (special characters):
The command number of this command. |
\#
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SHELL PROMPT (special characters):
The history number of this command. |
\!
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SHELL PROMPT (special characters):
The character corresponding to the octal number nnn. |
\nnn
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SHELL PROMPT (special characters):
If the effective uid is 0, #; otherwise, $. |
\$
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SHELL PROMPT (special characters):
A backslash. |
\\
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SHELL PROMPT (special characters):
Begin a sequence of nonprinting characters. |
\[
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SHELL PROMPT (special characters):
End a sequence of nonprinting characters. |
\]
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SHELL ARITHMETIC:
two formats for math expansion |
$[ expression ]
or $(( expression )) |
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SHELL ARITHMETIC:
builtin for performing math on variables |
let
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SYNTAX:
"for" loop statement (simple) |
for name in word1 word2 ... wordN
do list done OR: for name in wordlist; do list; done |
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SYNTAX:
"until" loop statement (simple) |
until [ condition ]
do list done OR: until cmd; do list; done |
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SYNTAX:
"while" loop statement (simple) |
while [ condition ]
do list done OR: while test-cmd; do list; done |
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SYNTAX:
"case" flow control statement (simple) |
case word in
pattern1) list1 ;; pattern2) list2 ;; pattern3) list2 ;; patternN) list-N ;; esac |
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SYNTAX:
"if then else" flow control statement |
if [ condition ]
then perform-list-2 elif [ condition ] then perform-list-4 else perform-list-5 fi |
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Login Banner location?
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/etc/issue
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Message of the day (at login)?
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/etc/motd
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If this file exists, ONLY root may login.
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/etc/nologin
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If this file exists, login is quiet.
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.hushlogin
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database of users currently logged in?
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/var/run/utmp
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Store login and logout history?
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/var/log/wtmp
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File that defines which ttys that root may log in from.
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/etc/securetty
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COMMAND:
...that will set terminal config values. |
setterm
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COMMAND:
...display or set tty config values |
stty
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COMMAND:
...display information about filesystems |
df
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KERNEL:
...program to add and remove modules from the linux kernel |
modprobe
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KERNEL:
...a module to create a module dependency list. |
depmod (creates modules.dep)
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KERNEL:
...simple tool for installing modules |
insmod (modprobe is "cleverer")
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KERNEL:
...show the status of modules in the Linux kernel |
lsmod
(formats contents of /proc/modules) |
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KERNEL:
...remove modules from kernel |
rmmod
OR modprobe -r |
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COMMAND:
...concatenate and print files in reverse |
tac (remember cat backwards)
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COMMAND:
...reverse lines |
rev (think forward = drawrof)
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COMMAND:
...compare two sorted files line by line |
comm
(this outputs common lines) |
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COMMAND:
..compare two files, usually binary files |
cmp
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COMMAND:
...find the difference between two files |
diff
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COMMAND:
...find the difference between three files |
diff3
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COMMAND:
...merge differences between two files (interactively) |
sdiff
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COMMAND:
...columnate input |
column
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COMMAND:
...remove columns from a file |
colrm
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COMMAND:
...split a file into sections determined by context lines |
csplit
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COMMAND:
...remove sections from each line of files |
cut
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COMMAND:
...convert tabs to spaces |
expand
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COMMAND:
...Reformat each paragraph (width) in the FILE(s), writing to standard output. |
fmt
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COMMAND:
... wrap each input line to fit in specified width |
fold
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COMMAND:
...merge lines of files. Write lines consisting of the sequentially corresponding lines from each FILE, separated by TABs, to standard output. |
paste
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COMMAND:
... split a file into pieces |
split
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COMMAND:
...Translate, squeeze, and/or delete characters from standard input, writing to standard output. |
tr
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COMMAND:
... convert spaces to tabs |
unexpand
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COMMAND:
...Discard all but one of successive identical lines from INPUT |
uniq
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COMMAND:
...show current run level |
runlevel
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COMMAND:
...display bootup messages |
dmesg
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COMMAND:
...add a job to the scheduling queue. |
at
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COMMAND:
...display the contents of the scheduling queue. |
atq
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COMMAND:
...remove a job from the scheduling queue. |
atrm.
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COMMAND:
...wait some number of seconds |
sleep n
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COMMAND:
...wait some number of micro-seconds |
usleep n
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COMMAND:
... batch executes commands when system load levels permit; in other words, when the load average drops below 0.8, or the value specified in the invocation of atrun. |
batch
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FILE:
..defines users permitted to use 'at' |
/etc/at.allow
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FILE:
...defines users permitted to use 'cron' |
/etc/cron.allow
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FILE:
...defines users NOT permitted to use 'at' |
/etc/cron.deny
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FILE:
...defines users NOT permitted to use 'cron.deny' |
/etc/cron.deny
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|
FILE:
..contains system load average |
/proc/loadavg
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COMMAND:
...display amount of free and used memory in the system |
free
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COMMAND:
...graphic representation of system load average |
tload
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COMMAND:
...report virtual memory statistics |
vmstat
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COMMAND:
...display shared memory, semaphores, message queues. |
ipcs
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COMMAND:
...an encryption and signing tool |
gpg (GNU Privacy Guard)
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COMMAND:
...a signature verification tool |
gpgv
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COMMAND:
...display a calendar |
cal
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COMMAND:
... a spell checker designed to eventually replace Ispell. It can either be used as a library or as an independent spell checker. |
aspell
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OSI Reference Model
...layers? (just another reminder :-) |
1. Physical
2. Data Link 3. Network 4. Transport 5. Session 6. Presentation 7. Application |
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TCP MODEL
..."five layer Internet Model" |
5. Application
4. Transport 3. Network 2. Data Link 1. Physical |
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COMMAND:
...network status information |
netstat
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COMMAND:
...display and manipulate routing information |
route
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FILE:
...contains Internet services by number |
/etc/services
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FILE:
...contains DNS server information |
/etc/resolv.conf
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COMMANDS:
...is a program to maintain identical copies of files over multiple hosts. |
rdist
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COMMAND:
...list open files for a user |
lsof -u username
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COMMAND:
...list active processes for a particular program |
lsof -c sshd (example)
|