Linux check exist user

Linux: Check if a User or a Group Exists 2

You can find out if user exists by searching in the /etc/passwd file using the following command:

egrep -i "^useraccount:" /etc/passwd

The above command will print the matching record from /etc/passwd if the user exists or nothing if the user does not exist.
The ^ symbol is used to make sure there is no characters before the username and the : character is used as the delimiter in the file (which indicates the end of the username). By wrapping the username with these characters we are sure that if we matched a record, we matched the correct record with the full username.

A very simple way to use this code in a script is by utilizing the $? (question mark) variable. The question mark variable contains the exit status of the last command that executed. Specifically, egrep will return 0 if there was a match or else it will return a a positive number (usually 1).
Taking advantage of this behavior, after executing the above command, we check the $? variable to see the result with an if statement.

egrep -i "^useraccount:" /etc/passwd; if [ $? -eq 0 ]; then echo "User Exists" else echo "User does not exist -- Invalid Username" fi

You can also find out if a group exists by searching in the /etc/group file. Similar to the approach we showed before, we can check if a group exists using the following:

egrep -i "^groupname" /etc/group; if [ $? -eq 0 ]; then echo "Group Exists" else echo "Group does not exist -- Invalid Group name" fi

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Check if user exists

user infomation is stored in /etc/passwd, so you can use «grep ‘usename’ /etc/passwd» to check if the username exist. meanwhile you can use «id» shell command, it will print the user id and group id, if the user does not exist, it will print «no such user» message.

What is the command to list all users in Linux?

Method # 1: The “cat” command

Use the “cat” command to list all the users on the terminal to display all the user account details and passwords stored in the /etc/passwd file of the Linux system. As shown below, running this command will display the usernames, as well as some additional information.

How do I know my username in Linux?

To quickly reveal the name of the logged in user from the GNOME desktop used on Ubuntu and many other Linux distributions, click the system menu in the top-right corner of your screen. The bottom entry in the drop-down menu is the user name.

What is usermod command in Linux?

The usermod command is one of the several Linux commands system administrators have at their disposal for user management. It is used to modify existing user account details, such as username, password, home directory location, default shell, and more.

How do I list users in Unix?

To list all users on a Unix system, even the ones who are not logged in, look at the /etc/password file. Use the ‘cut’ command to only see one field from the password file. For example, to just see the Unix user names, use the command “$ cat /etc/passwd | cut -d: -f1.”

How do I see users in Ubuntu?

Listing users in Ubuntu can be found in the /etc/passwd file. The /etc/passwd file is where all your local user information is stored. You can view the list of users in the /etc/passwd file through two commands: less and cat.

How do I see all users and groups in Linux?

In order to list users on Linux, you have to execute the “cat” command on the “/etc/passwd” file. When executing this command, you will be presented with the list of users currently available on your system. Alternatively, you can use the “less” or the “more” command in order to navigate within the username list.

What does \b do in grep?

\b in a regular expression means «word boundary». With this grep command, you are searching for all words i in the file linux. txt . i can be at the beginning of a line or at the end, or between two space characters in a sentence.

What command is used to check the current users?

‘W’ command is used to check the current users.

What is Getent used for?

getent is a Unix command that helps a user get entries in a number of important text files called databases. This includes the passwd and group databases which store user information – hence getent is a common way to look up user details on Unix.

What is Gpasswd in Linux?

The gpasswd command is used to administer /etc/group, and /etc/gshadow. Every group can have administrators, members and a password. System administrators can use the -A option to define group administrator(s) and the -M option to define members. They have all rights of group administrators and members.

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Find out if user name exists

How can I find out, in a shell script, whether a given user name exists on the current system? /etc/passwd and /etc/shadow are incomplete. Consider OS X’s Directory Services, or Linux with Likewise Active Directory integration.

4 Answers 4

One of the most basic tools to be used for that is probably id .

#!/bin/bash if id "$1" >/dev/null 2>&1; then echo "user exists" else echo "user does not exist" fi 

$ ./userexists root user exists $ ./userexists alice user does not exist $ ./userexists user does not exist 

This command is designed to gather entries for the databases that can be backed by /etc files and various remote services like LDAP, AD, NIS/Yellow Pages, DNS and the likes.

To figure out if a username is known by one of the password naming services, simply run:

This works also with group, hosts and others, depending on the OS and implementation.

While Solaris and Linux, and more recently also most BSDs have getent , there is no getent on Mac OS X

finger

Parse the output of finger -m . No error code if no user was found, unfortunately, but if not found, error output will be written. No drawbacks so far.

finger -ms 2>&1 1>/dev/null | wc -l 

Will print 0 if user is found (because there’s no error output), larger numbers otherwise.

chown

Run (as any user, surprisingly):

T=$( mktemp -t foo.XXX ) ; chown $T 

If it fails as root , the account name is invalid.

If it fails as non- root user, parse the possibly localized output for Operation not permitted or invalid user (or equivalents). Set LANG beforehand to do this reliably.

I would say that you would want to rely on /etc/passwd and similar (e.g. /etc/shadow for Shadow-based systems; on an off-topic side-note, some similar systems might use /etc/master.passwd or other such files).

The /etc/passwd is typically treated as the absolute authoritative decision on whether a user exists or not. If you use any of the other methods described on this page, and if those other methods point to an existing user but /etc/passwd does not, then I would say that the user does not properly exist on the system, by definition of the most common standard that software would likely rely on.

That said, I’ll throw in another way to add to the mix of some other options that could be used.

ls -l /home | grep ^customUserName$ echo $?

Clearly, replace «customuserName» with the name of the user you want to check for. Replace /home with /users if that is what your system uses. This might not find all users in /etc/passwd if no home directory was made for the particular user, which could occur if you simply imported users (that is, lines of text into /etc/passwd) and if home directories don’t get made unless/until a person logs in.

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Linux Check User: How to Verify User Existence

As a system administrator, one of the most crucial tasks is to manage users on a Linux system. Linux provides various tools to manage users, such as useradd, usermod, and userdel. However, before you can manage a user, you need to make sure that the user exists on the system. In this article, we will […]

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As a system administrator, one of the most crucial tasks is to manage users on a Linux system. Linux provides various tools to manage users, such as useradd , usermod , and userdel . However, before you can manage a user, you need to make sure that the user exists on the system. In this article, we will discuss how to check if a user exists on a Linux system.

Checking User Existence

To check if a user exists on a Linux system, we can use the id command. The id command is used to display user and group information for a specified user. If the user exists, the command will display the user’s UID (user ID) and GID (group ID) along with other information. If the user does not exist, the command will display an error message.

Here’s the basic syntax of the id command:

To check if a user exists, simply replace [username] with the username you want to check. For example, to check if the user john exists, you can run the following command:

If the user exists, the output will look something like this:

uid=1000(john) gid=1000(john) groups=1000(john),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),116(lpadmin),126(sambashare)

If the user does not exist, the command will display an error message like this:

Checking User Existence with Shell Script

You can also check for user existence using a shell script. Here’s an example shell script that checks for the existence of a user:

#!/bin/bash if id "$1" >/dev/null 2>&1; then echo "User exists" else echo "User does not exist" fi

Save the above code in a file named user-exists.sh and make it executable using the following command:

Now, to check if a user exists, simply run the script and pass the username as an argument:

If the user exists, the script will output User exists . If the user does not exist, the script will output User does not exist .

Conclusion

In conclusion, checking for user existence is an essential task for any Linux system administrator. In this article, we discussed how to check if a user exists on a Linux system using the id command and a shell script. By understanding these methods, you can easily verify the existence of a user and proceed with managing them as necessary.

Alex Ivanovs

Alex is a full-stack developer with more than 15 years of experience. After many years of threading the self-taught path, he discovered a natural passion for writing. His past work includes helping build the Huffington Post Code column and working with publishers such as Entrepreneur, TheNextWeb, and many prominent tech startups.

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