Validate the problem and find the problem

Verify in Manual Pageexec -c commandNo new process is started, but the environment variable is empty.

Verification method:

  1. Print process idecho $BASHPID
  2. Print the environment variable PATHecho $PATH

  3. Print all environment variables export-p

    // File test1 #! /usr/bin/bash set-e./test2 // Test2 #! /usr/bin/bash set -e echo '2==PID='$BASHPID echo '2==PPID='$PPID echo '2==PATH='$PATH echo '2==export=='`export -p` exec -c./test3 // File test3 #! /usr/bin/bash set-e echo '3==PID='$BASHPID 'echo '3==PPID='$PPID echo '3==PATH='$PATH echo '3==export='' export -p '// $ ./test1 2==PID=28697 2==PPID=28696 2==PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin 2==export==declare -x DBUS_SESSION_BUS_ADDRESS=" UNIX :path=/run/user/1000/bus" declare -x HOME=" user HOME "declare -x LANG=" en_us.utf-8 "declare -x LC_terminal ="iTerm2" declare -x LC_terminal_version ="3.3.8" declare -x LESSCLOSE = "/ usr/bin/lesspipe % s % s" declare - x LESSOPEN = "| / usr/bin/lesspipe % s" declare - x LOGNAME = "logged in user" declare - x LS_COLORS="rs=0:di=01; 34:ln=01; 36:mh=00:pi=40; 33:so=01; 35:do=01; 35:bd=40; 33. 01:cd=40; 33. 01:or=40; 31; 01:mi=00:su=37; 41:sg=30; 43:ca=30; 41:tw=30; 42:ow=34; 42:st=37; 44:ex=01; 32:*.tar=01; 31:*.tgz=01; 31:*.arc=01; 31:*.arj=01; 31:*.taz=01; 31:*.lha=01; 31:*.lz4=01; 31:*.lzh=01; 31:*.lzma=01; 31:*.tlz=01; 31:*.txz=01; 31:*.tzo=01; 31:*.t7z=01; 31:*.zip=01; 31:*.z=01; 31:*.dz=01; 31:*.gz=01; 31:*.lrz=01; 31:*.lz=01; 31:*.lzo=01; 31:*.xz=01; 31:*.zst=01; 31:*.tzst=01; 31:*.bz2=01; 31:*.bz=01; 31:*.tbz=01; 31:*.tbz2=01; 31:*.tz=01; 31:*.deb=01; 31:*.rpm=01; 31:*.jar=01; 31:*.war=01; 31:*.ear=01; 31:*.sar=01; 31:*.rar=01; 31:*.alz=01; 31:*.ace=01; 31:*.zoo=01; 31:*.cpio=01; 31:*.7z=01; 31:*.rz=01; 31:*.cab=01; 31:*.wim=01; 31:*.swm=01; 31:*.dwm=01; 31:*.esd=01; 31:*.jpg=01; 35:*.jpeg=01; 35:*.mjpg=01; 35:*.mjpeg=01; 35:*.gif=01; 35:*.bmp=01; 35:*.pbm=01; 35:*.pgm=01; 35:*.ppm=01; 35:*.tga=01; 35:*.xbm=01; 35:*.xpm=01; 35:*.tif=01; 35:*.tiff=01; 35:*.png=01; 35:*.svg=01; 35:*.svgz=01; 35:*.mng=01; 35:*.pcx=01; 35:*.mov=01; 35:*.mpg=01; 35:*.mpeg=01; 35:*.m2v=01; 35:*.mkv=01; 35:*.webm=01; 35:*.webp=01; 35:*.ogm=01; 35:*.mp4=01; 35:*.m4v=01; 35:*.mp4v=01; 35:*.vob=01; 35:*.qt=01; 35:*.nuv=01; 35:*.wmv=01; 35:*.asf=01; 35:*.rm=01; 35:*.rmvb=01; 35:*.flc=01; 35:*.avi=01; 35:*.fli=01; 35:*.flv=01; 35:*.gl=01; 35:*.dl=01; 35:*.xcf=01; 35:*.xwd=01; 35:*.yuv=01; 35:*.cgm=01; 35:*.emf=01; 35:*.ogv=01; 35:*.ogx=01; 35:*.aac=00; 36:*.au=00; 36:*.flac=00; 36:*.m4a=00; 36:*.mid=00; 36:*.midi=00; 36:*.mka=00; 36:*.mp3=00; 36:*.mpc=00; 36:*.ogg=00; 36:*.ra=00; 36:*.wav=00; 36:*.oga=00; 36:*.opus=00; 36:*.spx=00; 36:*.xspf=00; 36:" declare -x MOTD_SHOWN=" PAM "declare -x OLDPWD=" user directory" declare -x PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin" declare -x PWD=" Current DirectoryName "declare -x SHELL="/bin/bash" declare -x SHLVL="3" declare -x SSH_CLIENT="192.168.0.101 51426 22" declare -x SSH_CONNECTION="192.168.0.101 51426 192.168.0.121 22" declare -x SSH_TTY="/dev/pts/0" declare -x TERM="xterm-256color" Declare - x USER = "USER name" declare - x XDG_DATA_DIRS = "/ usr/local/share: / usr/share: / var/lib/snapd/desktop" declare - x XDG_RUNTIME_DIR="/run/user/1000" declare -x XDG_SESSION_CLASS="user" declare -x XDG_SESSION_ID="204" declare -x XDG_SESSION_TYPE="tty" 3==PID=28697 3==PPID=28696 3==PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin 3==export=declare -x OLDPWD declare -x PWD=" directory name "-x SHLVL="1"

Observe the output

Test2 has the same process ID and parent ID as Test3, whose environment variable (export-p) can be considered empty (PWD is the current directory name, SHLVL is the shell depth).

Echo $PATH = $PATH = $PATH = $PATH = $PATH = $PATH = $PATH = $PATH = $PATH;

What is the PATH output from querying test3

  • Search in the global environment because the environment variable is empty and inherits a global environment variable

    $ grep -rns /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin / /etc/environment:1:PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/ bin" /etc/login.defs:102:ENV_SUPATH PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin ^C

  • /etc/environment is only one line with no extra information, see /etc/login.defs comment

    # # * Required * The Default Path Settings, for SuperUser and Normal Users. Set the default PATH # # for superusers and regular users respectively (they are minimal, add the rest in the shell startup files) ENV_SUPATH PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin ENV_PATH PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games

  • A Bing search also found an answer to what is ENV_SUPATH

    https://unix.stackexchange.com/questions/317338/etc-login-defs-env-path-env-supath-vs-path

reference

  • Bash Reference Manual：https://www.gnu.org/software/…
  • The/etc/login. Defs: ENV_PATH & ENV_SUPATH vs PATH: https://unix.stackexchange.co…