怎么会找不到命令bash: Is :找不到命令

如题
今天准备安装软件，先是下载了一个tz包，上网查如何安装，结果装了半截，用到make命令时，显示文件不存在，然后使用Is命令，结果出现如下状况：



jun@jun-laptop:~$ Is
bash: Is：找不到命令
jun@jun-laptop:~$ cd /media
jun@jun-laptop:/media$ Is
bash: Is：找不到命令
jun@jun-laptop:/media$ ./Is
bash: ./Is: 没有该文件或目录
jun@jun-laptop:/media$ is
bash: is：找不到命令
jun@jun-laptop:/media$ ./is
bash: ./is: 没有该文件或目录
jun@jun-laptop:/media$ help
GNU bash, version 3.2.39(1)-release (i486-pc-linux-gnu)
shell 的命令是内置定义的，输入 “help” 可以看到这个列表。
输入“help name” 来查找关于 “name”命令功能的更多信息。
输入 “info bash” 来查看关于 shell 的更多信息。
输入 “man -k” 或者 “info” 来查看没有列在这个列表中的命令的信息。
带有星号(*)的命令是被禁止的。

JOB_SPEC [&] (( expression ))
. filename [arguments] :
[ arg... ] [[ expression ]]
alias [-p] [name[=value] ... ] bg [job_spec ...]
bind [-lpvsPVS] [-m keymap] [-f fi break [n]
builtin [shell-builtin [arg ...]] caller [EXPR]
case WORD in [PATTERN [| PATTERN]. cd [-L|-P] [dir]
command [-pVv] command [arg ...] compgen [-abcdefgjksuv] [-o option
complete [-abcdefgjksuv] [-pr] [-o continue [n]
declare [-afFirtx] [-p] [name[=val dirs [-clpv] [+N] [-N]
disown [-h] [-ar] [jobspec ...] echo [-neE] [arg ...]
enable [-pnds] [-a] [-f filename] eval [arg ...]
exec [-cl] [-a name] file [redirec exit [n]
export [-nf] [name[=value] ...] or false
fc [-e ename] [-nlr] [first] [last fg [job_spec]
for NAME [in WORDS ... ;] do COMMA for (( exp1; exp2; exp3 )); do COM
function NAME { COMMANDS ; } or NA getopts optstring name [arg]
hash [-lr] [-p pathname] [-dt] [na help [-s] [pattern ...]
history [-c] [-d offset] [n] or hi if COMMANDS; then COMMANDS; [ elif
jobs [-lnprs] [jobspec ...] or job kill [-s sigspec | -n signum | -si
let arg [arg ...] local name[=value] ...
logout popd [+N | -N] [-n]
printf [-v var] format [arguments] pushd [dir | +N | -N] [-n]
pwd [-LP] read [-ers] [-u fd] [-t timeout] [
readonly [-af] [name[=value] ...] return [n]
select NAME [in WORDS ... ;] do CO set [--abefhkmnptuvxBCHP] [-o opti
shift [n] shopt [-pqsu] [-o long-option] opt
source filename [arguments] suspend [-f]
test [expr] time [-p] PIPELINE
times trap [-lp] [arg signal_spec ...]
true type [-afptP] name [name ...]
typeset [-afFirtx] [-p] name[=valu ulimit [-SHacdfilmnpqstuvx] [limit
umask [-p] [-S] [mode] unalias [-a] name [name ...]
unset [-f] [-v] [name ...] until COMMANDS; do COMMANDS; done
variables - Some variable names an wait [n]
while COMMANDS; do COMMANDS; done { COMMANDS ; }
jun@jun-laptop:/media$

Is命令是我第一次用