Why am I getting errors in this script?

Question

I am currently trying to implement this script given as the accepted answer on this question. Now I have created the script change_wallpaper_reddit.sh, and the script is below for your convenience.

# Reference: https://askubuntu.com/a/911958/566421

# Set the script home directory:
SHOME=Daily-Reddit-Wallpaper

# Set the output folder in the home directory to save the Wallpapers to:
DIR=Pictures/Wallpapers

# Set the --time parameter value
TIME=now

# Check if the Desktop Environment is changed:
LAST=$(cat "$HOME/$SHOME/last-desktop-environment.log")
if [ "$1" != "$LAST" ]
then
    # Get the name of the last saved wallpaper image:
    IMG=$(ls -Art $HOME/$DIR | tail -n 1)
    rm $HOME/$DIR/$IMG
fi

# Desktop Environment cases:
if [ -z ${1+x} ] || [ "$1" = "gnome" ] || [ "$1" = "unity" ]
then
    # Set the necessary environment variables - PID=$(pgrep gnome-session -u $USER) - UBUNTU/UNITY/GNOME:
    export GNOME_DESKTOP_SESSION_ID=true
    export DBUS_SESSION_BUS_ADDRESS=$(grep -z DBUS_SESSION_BUS_ADDRESS /proc/$(pgrep gnome-session -n)/environ | cut -d= -f2-)

    # Run the script:
    ~/$SHOME/change_wallpaper_reddit.py --time $TIME --output ~/$DIR 

elif [ "$1" = "kde" ]
then
    # Set the necessary environment variables - KUBUNTU/PLASMA/KDE:
    export KDE_FULL_SESSION=true
    export DBUS_SESSION_BUS_ADDRESS=$(grep -z DBUS_SESSION_BUS_ADDRESS /proc/$(pgrep startkde -n)/environ | cut -d= -f2-)

    # Run the script:
    $HOME/$SHOME/change_wallpaper_reddit.py --time $TIME --output $DIR

elif [ "$1" = "mate" ]
then
    # Set the necessary environment variables - Ubuntu MATE/MATE:
    export DESKTOP_SESSION=mate
    export DBUS_SESSION_BUS_ADDRESS=$(grep -z DBUS_SESSION_BUS_ADDRESS /proc/$(pgrep mate-session -n)/environ | cut -d= -f2-)

    # Run the script:
    $HOME/$SHOME/change_wallpaper_reddit.py --time $TIME --output $DIR

elif [ "$1" = "lxde" ]
then
    # Set the necessary environment variables - type 'echo $DISPLAY` to find your current display - LUBUNTU/LXDE:
    export DESKTOP_SESSION=Lubuntu
    export DBUS_SESSION_BUS_ADDRESS=$(grep -z DBUS_SESSION_BUS_ADDRESS /proc/$(pgrep lxsession -n)/environ | cut -d= -f2-)
    export DISPLAY=:1.0

    # Run the script:
    $HOME/$SHOME/change_wallpaper_reddit.py --time $TIME --output $DIR

elif [ "$1" = "xfce4" ]
then
    # Set the necessary environment variables - XUBUNTU/XFCE4:
    export DBUS_SESSION_BUS_ADDRESS=$(grep -z DBUS_SESSION_BUS_ADDRESS /proc/$(pgrep xfce4-session -n)/environ|cut -d= -f2-)

    # Run the script:
    $HOME/$SHOME/change_wallpaper_reddit.py --time $TIME --output $DIR

    # Get the name of the last saved wallpaper image:
    IMG=$(ls -Art $HOME/$DIR | tail -n 1)

    # Since 'change_wallpaper_reddit.py' doesn't work properly with xfce4 we shall set the background manually:
    xfconf-query --channel xfce4-desktop --property /backdrop/screen0/monitor0/workspace0/last-image --set $HOME/$DIR/$IMG

    # Property list:      xfconf-query --channel xfce4-desktop --list
    # Current settings:   xfconf-query -c xfce4-desktop -p /backdrop -lv
    # Set 'zoomed' style: xfconf-query --channel xfce4-desktop --property /backdrop/screen0/monitor0/workspace0/image-style --set 5
    # References:         https://askubuntu.com/q/380550/566421 and https://askubuntu.com/q/414422/566421

else
    echo "Wrong argument. It must be:"
    echo "  - empty (default) = gnome = unity"
    echo "  - kde"
    echo "  - lxde"
    echo "  - mate"
    echo "  - xfce4"
fi

# Save the current value of the Desktop Environment variable:
echo "$1" > "$HOME/$SHOME/last-desktop-environment.log"

I have created a new job in my sudo crontab, as shown below:

0 * * * * /home/sharan/Daily-Reddit-Wallpaper/change_wallpaper_reddit.sh gnome > /home/sharan/Daily-Reddit-Wallpaper/cron.log 2>&1

However, this script isn't working and gives me the errors below, in the cron.log file.

cat: /root/Daily-Reddit-Wallpaper/last-desktop-environment.log: No such file or directory
ls: cannot access '/root/Pictures/Wallpapers': No such file or directory
rm: cannot remove '/root/Pictures/Wallpapers/': No such file or directory
/home/sharan/Daily-Reddit-Wallpaper/change_wallpaper_reddit.sh: 29: /home/sharan/Daily-Reddit-Wallpaper/change_wallpaper_reddit.sh: /root/Daily-Reddit-Wallpaper/change_wallpaper_reddit.py: not found
/home/sharan/Daily-Reddit-Wallpaper/change_wallpaper_reddit.sh: 88: /home/sharan/Daily-Reddit-Wallpaper/change_wallpaper_reddit.sh: cannot create /root/Daily-Reddit-Wallpaper/last-desktop-environment.log: Directory nonexistent

I don't exactly understand what is going wrong here.

shebang is missing, other then that are you sure you want to run it as root? you have to add that script to your crontab, each user has it's own. You can adjust your own by typing crontab -e without the sudo. — Ziazis, May 31 '17 at 12:10
Why not? Seems obvious to me that you are running the script as "root" and not as the user it is intended for.
"cat: /root/" error says you are running "root". So do the other errors. — Rinzwind, May 31 '17 at 12:11

score 3 · Accepted Answer · answered May 31 '17 at 12:11

3

You run the cron job as root, while expecting to work within a user's home directory. The problem is visible in this line:

LAST=$(cat "$HOME/$SHOME/last-desktop-environment.log")

where $HOME gets translated to /root/ and $SHOME to Daily-Reddit-Wallpaper. Then cat complains that there is no file /root/Daily-Reddit-Wallpaler/last-desktop-environment.log.

answered May 31 '17 at 12:11

Jos

29,224

Added the same cronjob to crontab and removed it from sudo crontab, yet the errors in cron.log are the same. – SDG May 31 '17 at 12:27
Really exactly the same? $HOME should now point to /home/sharan and not to /root. Something must have changed. – Jos May 31 '17 at 12:47
Looks like cron.log did not update. Now I get an error with the module praw missing, but I shall look into it/ post a different question. – SDG May 31 '17 at 13:55

Why am I getting errors in this script?

1 Answers1