How to allow a custom service script in RHEL7 to run in the foreground and accept user input

How to allow a custom service script in RHEL7 to run in the foreground and accept user input

https://access.redhat.com/solutions/1466153

 SOLUTION 已验证 - 已更新 2019年三月14日06:49 - 

English 

环境

• Red Hat Enterprise Linux 7

问题

• How to start a script at boot time in the foreground and let it accept keyboard input?

决议

NOTE: Red Hat does not support implementation of custom scripts, including custom systemd startup scripts. This article is provided as a how-to and Red Hat will not troubleshoot any issues after the implementation of the steps provided here. For more information please see the Production Support Scope of Coverage
See also: man systemd-ask-password

1. Create a new service unit file at /etc/systemd/system/example.service1 with content based on the following

   Raw

   [Unit]
   Description=Example Interactive Service Script description goes here
   After=network.target
   Before=sshd.service systemd-logind.service getty@tty1.service
   
   [Service]
   Type=oneshot
   TTYPath=/dev/tty13
   ExecStartPre=/usr/bin/chvt 13
   ExecStart=/usr/local/sbin/example.sh
   ExecStartPost=/usr/bin/chvt 1
   TimeoutStartSec=0
   StandardInput=tty
   TTYVHangup=yes
   TTYVTDisallocate=yes
   
   [Install]
   WantedBy=default.target
   RequiredBy=sshd.service systemd-logind.service getty@tty1.service
   

   Optionally, consult footnotes of individual arguments for explanation:
   After=2 Before=3 TTYPath=4 ExecStartPre=/usr/bin/chvt 135 ExecStart=6 ExecStartPost=/usr/bin/chvt 17 TimeoutStartSec=8StandardInput=tty9 TTYVTDisallocate=10

2. Create the example shell script mentioned in the unit file's ExecStart directive
   For example, save the following to /usr/local/sbin/example.sh, making sure the file is executable

   Raw

   #!/bin/bash
   until [[ -n ${REPLY} ]]; do
       read -ep "Enter your name: "
   done
   echo "WELCOME ${REPLY^^}"; sleep 5
   

3. Enable the service and then reboot to test

   Raw

   systemctl enable example.service
   reboot
   

---

1. The file should be located in either /usr/lib/systemd/system/ or /etc/systemd/system/. See UNIT LOAD PATH section in  man systemd.unit. ↩

2. After=   If the script needs any other system facilities (networking, etc), modify the [Unit] section to include appropriate After=, Wants=, or Requires= directives, as described in:  man systemd.unit ↩

3. Before=   If the script needs to be run before other services--for example, prior to starting sshd or console/graphical logins--ensure there is a Before=XYZ.service in the [Unit] section and a corresponding RequiredBy=XYZ.service in the [Install] section. For more discussion, see: How to prevent console and ssh logins until a service has started in RHEL7. ↩

4. TTYPath=   Specify a tty number here (the writer's choice of tty13 here was mostly arbitrary; however, keep in mind that numbers higher than 12 require the chvt command to access them). ↩

5. ExecStartPre=/usr/bin/chvt 13   This changes the physical console to tty13 (i.e., the tty specified with TTYPath=). ↩

6. ExecStart=   The full path to the main script, including any desired script arguments. ↩

7. ExecStartPost=/usr/bin/chvt 1   This changes the physical console back to tty1 after the script finishes (this line is not always necessary, e.g., if a display manager starts after the script, it will probably steal focus by changing the physical console back to whichever tty it is running on). ↩

8. TimeoutStartSec=   When a service doesn't signal start-up completion within TimeoutStartSec, systemd considers the service failed; for long-running shell scripts it is essential to modify TimeoutStartSec or disable the timeout logic altogether as above, with TimeoutStartSec=0. See  man systemd.service  for more details. ↩

9. StandardInput=tty   This line is absolutely necessary; without specifying the value tty here, this setting defaults to null. (Note that StandardOutput= and StandardError= can also be independently set; however, by default they inherit their value from StandardInput=.) See  man systemd.exec  for more details. ↩

10. TTYVTDisallocate=   When set to yes, this causes the tty (TTYPath) to be cleared before and after use. ↩