[SOLVED] Assigning UID's from specific range and in sequence RHEL 7

RedMan1001001 · 10-01-2020, 10:57 PM

Hi All,

Sorry if this is the wrong section - I am a Linux Newbie and need some help

I am writing a bash script to allow users to create new accounts using the 'useradd' command. The problem i have is I need the UID assigned from a specific range and in sequence.

For example, user runs the script and creates an new account with UID of 5000. Then user runs the script again however this time the UID assigned should be 5001. If 5001 is not available then it should select 5002 automatically.

Does anyone know how i can achieve this?

This is what i have so far:

Code:

#!/bin/bash

uarray=($(seq 5000 5049))

n=0

read -p "username : " i

   if ! grep $i /etc/passwd >/dev/null; then
             useradd -u ${uarray[$n]} -g system_user -c "Regular User" $i
                echo $?
                if [[ $? -eq 4 ]]; then
                        while [[ $? -eq 4 ]]
                        do
                        UID=`expr "$n" + 1`
                        useradd -u ${uarray[$UID]} -g system_user -c "Regular User" $i
                        echo $?
                        done
               fi
   fi

The above code creates a user with UID of 5000 but then when i re-run the script it doesn't increment to the next UID available.

i am writing this is BASH and am running RHEL 7.9

I'm no scripting expert by any means and i've almost pulled out all my hair trying to make this work. Any help will be appreciated.

berndbausch · 10-02-2020, 06:29 AM

The problem is probably that $? always contains the result of the most recent command. Therefore, in the if condition, it contains the result of the echo command, which is 0. Your program never enters the while loop.

Fix this by saving $? to a variable. That's all you need, I think.

A few suggestions for a prettier and easier to read script:

Rather than redirecting grep's output, use grep -q.
You don't need the if [[ $? -eq 4 ]]. Remove it entirely.
Arithmetic looks prettier like this: while (($?==4))
No need to use expr, rather: UID=$((n+1)) (look, ma, no $ sign!)

scasey · 10-02-2020, 06:54 AM

A. That’s how useradd should work out of the box. You shouldn’t need to anything special in your script. Is it not working that way for you?
B. Have you looked at RedHat’s support documentation and/or contacted their support? You’re paying for it, yes?

michaelk · 10-02-2020, 08:57 AM

To expand on berndbausch suggestions you can simplify your loops and get rid of the array.

Untested code...

Code:

for ((n=5000;n<5050;n++)); do
    useradd -u $n ...
    if [[ $? -eq 0 ]]; then
       echo "$i added successfully"
       exit
    fi
done

With most distributions now UIDs for regular users start at 1000, if the OP wants something different you have specify it as an option.

RedMan1001001 · 10-02-2020, 09:10 AM

Quote:

Originally Posted by berndbausch

The problem is probably that $? always contains the result of the most recent command. Therefore, in the if condition, it contains the result of the echo command, which is 0. Your program never enters the while loop.

Fix this by saving $? to a variable. That's all you need, I think.

A few suggestions for a prettier and easier to read script:

Rather than redirecting grep's output, use grep -q.
You don't need the if [[ $? -eq 4 ]]. Remove it entirely.
Arithmetic looks prettier like this: while (($?==4))
No need to use expr, rather: UID=$((n+1)) (look, ma, no $ sign!)

Thanks for the response!... I have updated the script with the suggestions you made - it looks like:

Code:

#!/bin/bash

uarray=($(seq 5000 5049))

n=0

read -p "type : " i

        if ! grep $i /etc/passwd >/dev/null; then

             useradd -u ${uarray[$n]} -g system_user -c "Regular User" $i

                        while (($?==4))

                        do

                        newuid=$((n+1))

                        useradd -u ${uarray[$newuid]} -g system_user -c "Regular User" $i

                        done
        fi

When i ran the above, it did select the next UID, so instead of 5000, it picked 5001 but then didnt move on to 5002 as 5001 was not available, it just kept looping between 5000 & 5001 and got stuck...

Code:

type : test4
useradd: UID 5000 is not unique
useradd: UID 5001 is not unique
useradd: UID 5001 is not unique
useradd: UID 5001 is not unique
useradd: UID 5001 is not unique
useradd: UID 5001 is not unique
useradd: UID 5001 is not unique
useradd: UID 5001 is not unique
....

What am i doing worng?

michaelk · 10-02-2020, 09:17 AM

See my post (#4) on simplifying your script a bit.

Why are you changing variable names?

Code:

n=$((n+1))
useradd -u ${uarray[$n]}...

RedMan1001001 · 10-02-2020, 09:18 AM

Quote:

Originally Posted by michaelk

To expand on berndbausch suggestions you can simplify your loops and get rid of the array.

Untested code...

Code:

for ((n=5000;n<5050;n++)); do
    useradd -u $n ...
    if [[ $? -eq 0 ]]; then
       echo "$i added successfully"
       exit
    fi
done

With most distributions now UIDs for regular users start at 1000, if the OP wants something different you have specify it as an option.

Thank you for this.

It worked perfectly.

For anyone else searching like i was, here's what i used:

Code:

read -p "username : " i

for ((n=5000;n<5050;n++)); do
    useradd -u $n -g system_user -c "Regular User" $i
    if [[ $? -eq 0 ]]; then
       echo "$i added successfully"
       exit
    fi
done

The result was:

Code:

username : test6
useradd: UID 5000 is not unique
useradd: UID 5001 is not unique
useradd: UID 5002 is not unique
useradd: UID 5003 is not unique
test6 added successfully

A quick cat on the passwd file confirmed it all worked ok:

Code:

test6:x:5004:1002:Regular User:/home/test6:/bin/bash

Thank you all for the help and advice. It is much appreciated.

michaelk · 10-02-2020, 09:25 AM

I left out your check to see if your username is unique and you might want to add something to indicate if all the UIDs in your sequence have been used.