30

I usually do

sleep 4h; command

to execute a command after 4h. However, if that command requires sudo, it'll not work.

Is it possible to give sudo permission at the moment I'm running the sleep command?

46

Use sudo to start a root shell where you run the commands:

sudo bash -c 'sleep 4h; command'

Every command running in the root shell runs with root permissions, which for sleep doesn’t hurt. If you need to run a command with user permissions in it, use sudo -u USERNAME COMMAND, e.g.:

$ sudo bash -c 'sleep 4h; sudo -u dessert whoami; whoami'
dessert  # whoami run as user dessert
root     # whoami run as root

Another approach would be to use sudo visudo to allow the command’s execution without root access, see: How to allow execution without prompting for password using sudo?
Note that depending on the command this may create a security flaw.

21

Assuming you only want to run the process once (not, e.g. every 4 hours) then you can use atd

  1. Ensure that atd is running (in ubuntu that is /etc/init.d/atd status or better still systemctl status atd)
  2. At a terminal as root run your command as follows:

    # at now + 4 hours
    warning: commands will be executed using /bin/sh
    at> command
    at> CTRL-D
    
  3. If you want to run it every 4 hours you could also use cron (as root) with the following config in your crontab

    0 */4 * * * sh -c $'/path/to/command'
    
  • 2
    Yes, at is the right tool for this job, because it also takes care of I/O redirection, doesn't block a shell window, and works even when the user has logged out or the machine has been rebooted since. – Simon Richter Feb 18 at 9:52
  • 4
    @SimonRichter: sudo bash -c 'sleep 4h && command' & to put sudo in the background is an easier way to not block a shell window / tab. If you want the output to pop up asynchronously as a reminder that it happened, that's easier. It doesn't work across reboots, but depending on your nohup settings it might stay running after exiting / logging out from a shell. – Peter Cordes Feb 18 at 12:56
  • 4
    Note that at runs the command as soon as it’s able to when the system is suspended at the specified time, see here on U&L – depending on the command(s) to run this may not be what you want. – dessert Feb 18 at 14:44
  • 2
    Just a suggestion, you can also use systemctl to check the service status instead of directly calling that init.d script. While both seemingly have the same result, I think the modern way of interacting with systemd services should be preferred: systemctl status atd – Byte Commander Feb 20 at 12:26
15

One way is to run via a shellscript with sudo permissions (and give the password, when you start the shellscript), if the shellscript is in the current directory,

sudo ./delayer 4h

where delayer can be a shellscript with the content

#!/bin/bash
sleep "$1"
command

Make it executable with

chmod +x delayer

and copy or move it to a directory in PATH if you wish.


If you want a more flexible shellscript, where you can select the command [line] to delay by entering parameter(s), you can try

#!/bin/bash

if [ $# -lt 2 ] || [ "$(whoami)" != "root" ]
then
 echo "Delay start of command, that needs 'sudo'
Usage:    sudo $0 <delay> <command line>
Example:  sudo $0 4h parted -ls"
 exit
fi

sleep "$1"
shift
"$@"

Demo example (short delay, 5s, for demo purpose),

$ ./delayer
Delay start of command, that needs 'sudo'
Usage:    sudo ./delayer <delay> <command line>
Example:  sudo ./delayer 4h parted -ls

$ sudo ./delayer 5s parted /dev/sdc p
[sudo] password for sudodus: 
Model: Kanguru SS3 (scsi)
Disk /dev/sdc: 15,9GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name     Flags
 2      1049kB  2097kB  1049kB               primary  bios_grub
 3      2097kB  258MB   256MB   fat32        primary  boot, esp
 4      258MB   2274MB  2016MB               primary
 5      2274MB  12,5GB  10,2GB  ext2         primary
 1      12,5GB  15,9GB  3394MB  ntfs         primary  msftdata
  • 3
    Well, if it's /bin/sh syntax it will be fine. But if you intend on using bash-specific features, then shebang is necessary. Me and steeldriver had discussion about that somewhere. Aaand Videonauth deleted his comment before I could respond properly. Oh well – Sergiy Kolodyazhnyy Feb 18 at 8:21
  • @SergiyKolodyazhnyy, You are right. So in this case the shebang is there to make the shellscript robust in case of added features where the syntax may differ. – sudodus Feb 18 at 8:27
  • @SergiyKolodyazhnyy Well it was just a suggestion so I thought leaving the comment there was not necessary and would only add to clutter. Feel free to hit me up in chat and point out your view :) – Videonauth Feb 18 at 10:10
2

Another way would be to start sudo interactive session with sudo -s (does not change directory) or sudo -i (changes current directory to root home directory) and then enter your commands (without sudo)

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.