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「掛起」指令在 Ubuntu 14 上有什麼作用？

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「掛起」指令在 Ubuntu 14 上有什麼作用？

我昨天安裝了 Ubuntu 14。無意中遇到了這個suspend命令。當我在命令列中輸入它並按 Enter 時，終端掛起。我既不能通過CTRL+中斷它C，也不能使用該名稱運行的進程kill。顯然，這不是一個腳本，因為 和 都which suspend傳回whereis suspend空結果：

void@wladiwostok ~ $ which suspend
void@wladiwostok ~ $ whereis suspend
suspend:

所以我認為這suspend一定是某種「內建」指令之類的exit東西。我是在想，出於好奇， 它有什麼作用？

我無法透過線上找到任何相關信息，因為大多數搜尋請求都為我提供了有關如何暫停電腦。

答案1

suspend是一個 shell 內建指令：

怎麼知道呢？

在任何命令之前運行命令類型以告訴您該命令是什麼：

$ type suspend

suspend is a shell builtin

若要取得 shell 內建指令的協助，請使用help

help suspend

suspend: suspend [-f]
    Suspend shell execution.
    
    Suspend the execution of this shell until it receives a SIGCONT signal.
    Unless forced, login shells cannot be suspended.
    
    Options:
      -f    force the suspend, even if the shell is a login shell
    
    Exit Status:
    Returns success unless job control is not enabled or an error occurs.

要列出所有內建命令，只需執行help不含選項的命令。

help

輸出是：

job_spec [&]                            history [-c] [-d offset] [n] or hist>
 (( expression ))                        if COMMANDS; then COMMANDS; [ elif C>
 . filename [arguments]                  jobs [-lnprs] [jobspec ...] or jobs >
 :                                       kill [-s sigspec | -n signum | -sigs>
 [ arg... ]                              let arg [arg ...]
 [[ expression ]]                        local [option] name[=value] ...
 alias [-p] [name[=value] ... ]          logout [n]
 bg [job_spec ...]                       mapfile [-n count] [-O origin] [-s c>
 bind [-lpvsPVS] [-m keymap] [-f filen>  popd [-n] [+N | -N]
 break [n]                               printf [-v var] format [arguments]
 builtin [shell-builtin [arg ...]]       pushd [-n] [+N | -N | dir]
 caller [expr]                           pwd [-LP]
 case WORD in [PATTERN [| PATTERN]...)>  read [-ers] [-a array] [-d delim] [->
 cd [-L|[-P [-e]]] [dir]                 readarray [-n count] [-O origin] [-s>
 command [-pVv] command [arg ...]        readonly [-aAf] [name[=value] ...] o>
 compgen [-abcdefgjksuv] [-o option]  >  return [n]
 complete [-abcdefgjksuv] [-pr] [-DE] >  select NAME [in WORDS ... ;] do COMM>
 compopt [-o|+o option] [-DE] [name ..>  set [-abefhkmnptuvxBCHP] [-o option->
 continue [n]                            shift [n]
 coproc [NAME] command [redirections]    shopt [-pqsu] [-o] [optname ...]
 declare [-aAfFgilrtux] [-p] [name[=va>  source filename [arguments]
 dirs [-clpv] [+N] [-N]                  suspend [-f]
 disown [-h] [-ar] [jobspec ...]         test [expr]
 echo [-neE] [arg ...]                   time [-p] pipeline
 enable [-a] [-dnps] [-f filename] [na>  times
 eval [arg ...]                          trap [-lp] [[arg] signal_spec ...]
 exec [-cl] [-a name] [command [argume>  true
 exit [n]                                type [-afptP] name [name ...]
 export [-fn] [name[=value] ...] or ex>  typeset [-aAfFgilrtux] [-p] name[=va>
 false                                   ulimit [-SHacdefilmnpqrstuvx] [limit>
 fc [-e ename] [-lnr] [first] [last] o>  umask [-p] [-S] [mode]
 fg [job_spec]                           unalias [-a] name [name ...]
 for NAME [in WORDS ... ] ; do COMMAND>  unset [-f] [-v] [name ...]
 for (( exp1; exp2; exp3 )); do COMMAN>  until COMMANDS; do COMMANDS; done
 function name { COMMANDS ; } or name >  variables - Names and meanings of so>
 getopts optstring name [arg]            wait [id]
 hash [-lr] [-p pathname] [-dt] [name >  while COMMANDS; do COMMANDS; done
 help [-dms] [pattern ...]               { COMMANDS ; }

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