Linux username length

Linux username length

Devops & sysadmins: what is the maximum username length

Some utilities or systems, such as top, ps, w/who, finger, NFS, and various multi-platform directory systems (NIS/NIS+, SMB, CIFS, Kerberos), can impose shorter names or act inconsistently when faced with longer names, likely due to limitations of other/remote platforms. If the username is longer than 8 characters, many of the psutil commands will display a UID instead of the username.
Some utilities and applications can place arbitrary limitations on their users. For example, IBM’s DB2 appears to prevent users from logging in with usernames longer than eight characters: db2-l/length-of-username-permitted-on-db2-95-aix-6-3248147 http://database.ittoolbox.com/groups/technical-functional/db2-l/length-of-username-permitted-on-db2-95-aix-6-3248147
Longer usernames are possible, as other answers have explained, but another realistic explanation to keep it to a maximum of 8 characters is that ps(1) records numeric uids instead of usernames longer than 8 characters.
In this case, it will depend on /etc/passwd first, which might (sort of, via useradd/groupadd) have a 32-character limit on user/group names, and then sss (sssd), which is likely to have a much different limit (1024 it seems if backed by ActiveDirectory).

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A attribute called a user identifier, sometimes abbreviated to user ID or UID, is used by Unix-like operating systems to identify a user. The UID is used to decide which device resources a user has access to, along with the group identifier (GID) and other access control criteria. Textual user names are mapped to UIDs in the password format. Inodes of the Unix file system, running processes, tar files, and the now-defunct Network Information Service all store UIDs. The command-line command id returns the current user’s UID as well as additional details such as the user name, primary user group, and group identifier in POSIX-compliant environments (GID).
For most access checks, a process’s successful UID (euid) is used. It’s also the owner of any files generated by the operation. Depending on the semantics of the particular kernel implementation in use and probably the mount options used, a process’ successful GID (egid) affects access control and may also affect file creation. The group ownership given to a newly created file is unconditionally inherited from the group ownership of the directory in which it is created, according to BSD Unix semantics. A newly generated file is normally given the group ownership defined by the egid of the process that creates the file, according to AT&T UNIX System V semantics (also adopted by Linux variants). When the S ISGID (s-gid) permission is set for unique folders, most filesystems enforce a method to select whether BSD or AT&T semantics should be used for group ownership of newly generated files. 1st

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When configuring a Linux system for the first time, creating a user is crucial. Since it has access to the operating system and its setup, the root account is usually only used for administration. This is not a good idea, so it is recommended that accounts be created for specific purposes such as remote connection or laptop use.
User accounts give users their own $HOME directory and allow you (the root administrator) to monitor which user accounts have access to the operating system’s configuration. Using them enhances protection since they restrict the number of acts that can be taken and hence the amount of harm that can be done (even from accidental errors).
If no OPTIONS are specified, a home directory in /home/username> will be created by default, with the shell set to use the root account (ash by default), user ID and group ID 1000+, and the GECOS field Linux User,,,.
If —ingroup is not defined, the new user is given a new GID that corresponds to the UID. Adduser will fail if the GID corresponding to a specified UID already exists. As a result, new users’ primary group is set to “user’s private group” (UPG). It enables the use of a permissive umask (002) that renders new files group-writable by default, only to the user’s private group, but writable to an entire user group if saved in special set-group-id group folders.

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On Arch Linux, the maximum length for a new username appears to be 32 characters.

Users, groups and permissions in linux

# useradd -m 123456789012345678901234567890123456789012

Linux/unix username length limit

Is it likely that using such a long username will cause some issues?
Is it possible that choosing a username that long will cause any issues? Waan wrote:Is it possible that choosing a username that long will cause any problems?
Yes, some user sockets are stored in the homedir, and their filepaths can be up to 108 characters long.
Flatpak issue: if the username is longer than 17 characters, the socket path is too long.
Is it possible that picking a username that long will cause any problems? sabroad wrote:Waan wrote:Is it possible that picking a username that long will cause any problems?
Yes, some user sockets are stored in the homedir, and their filepaths can be up to 108 characters long.
Flatpak issue: if the username is longer than 17 characters, the socket path is too long.
Then I’m curious as to why it’s possible to build a 32-character username on Arch. Is it worth it to reinstall the whole system because my usernames are 32 characters long? Should I just use the command # userdel? Although I am not particularly concerned with protection, does having a long username that exceeds the maximum character limit expose security vulnerabilities? Please accept my apologies for my novice query.

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