Valid special characters allowed in a CentOS 7 username?












0















I'm trying to figure out how CentOS 7 identifies what is considered a valid character in a naming convention when a user account is created.



I was playing around with useradd to confirm my understanding of what CentOS considered valid characters in a user name.... and to my surprise the useradd command accepted '_' and '.'... Which got me wondering where valid/invalid characters are established in CentOS



The useradd man page in CentOS doesn't mention valid characters... And google searches said this is done with NAME_REGEX (For ubuntu at least)... and had me looking for it in a adduser.conf file... which does not exist in CentOS 7... I haven't been able to locate a CentOS/Red Hat specific source on google about this... But I've also looked in /etc/login.defs and /etc/default/useradd with no luck



Can anyone direct me to the mechanism in CentOS does this?






centos users







share|improve this question




















  • 1





    Related, over at SO (for whatever reason): What are the real rules for linux usernames on CentOS 6 and RHEL 6?

    – Kusalananda
    5 hours ago











  • Relating unix.stackexchange.com/q/287077/117549

    – Jeff Schaller
    5 hours ago
















0















I'm trying to figure out how CentOS 7 identifies what is considered a valid character in a naming convention when a user account is created.



I was playing around with useradd to confirm my understanding of what CentOS considered valid characters in a user name.... and to my surprise the useradd command accepted '_' and '.'... Which got me wondering where valid/invalid characters are established in CentOS



The useradd man page in CentOS doesn't mention valid characters... And google searches said this is done with NAME_REGEX (For ubuntu at least)... and had me looking for it in a adduser.conf file... which does not exist in CentOS 7... I haven't been able to locate a CentOS/Red Hat specific source on google about this... But I've also looked in /etc/login.defs and /etc/default/useradd with no luck



Can anyone direct me to the mechanism in CentOS does this?






centos users







share|improve this question




















  • 1





    Related, over at SO (for whatever reason): What are the real rules for linux usernames on CentOS 6 and RHEL 6?

    – Kusalananda
    5 hours ago











  • Relating unix.stackexchange.com/q/287077/117549

    – Jeff Schaller
    5 hours ago














0












0








0








I'm trying to figure out how CentOS 7 identifies what is considered a valid character in a naming convention when a user account is created.



I was playing around with useradd to confirm my understanding of what CentOS considered valid characters in a user name.... and to my surprise the useradd command accepted '_' and '.'... Which got me wondering where valid/invalid characters are established in CentOS



The useradd man page in CentOS doesn't mention valid characters... And google searches said this is done with NAME_REGEX (For ubuntu at least)... and had me looking for it in a adduser.conf file... which does not exist in CentOS 7... I haven't been able to locate a CentOS/Red Hat specific source on google about this... But I've also looked in /etc/login.defs and /etc/default/useradd with no luck



Can anyone direct me to the mechanism in CentOS does this?






centos users







share|improve this question
















I'm trying to figure out how CentOS 7 identifies what is considered a valid character in a naming convention when a user account is created.



I was playing around with useradd to confirm my understanding of what CentOS considered valid characters in a user name.... and to my surprise the useradd command accepted '_' and '.'... Which got me wondering where valid/invalid characters are established in CentOS



The useradd man page in CentOS doesn't mention valid characters... And google searches said this is done with NAME_REGEX (For ubuntu at least)... and had me looking for it in a adduser.conf file... which does not exist in CentOS 7... I haven't been able to locate a CentOS/Red Hat specific source on google about this... But I've also looked in /etc/login.defs and /etc/default/useradd with no luck



Can anyone direct me to the mechanism in CentOS does this?






centos users




centos users






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 5 hours ago









Rui F Ribeiro

41.6k1483141




41.6k1483141










asked 5 hours ago









BodishaBodisha

282




282








  • 1





    Related, over at SO (for whatever reason): What are the real rules for linux usernames on CentOS 6 and RHEL 6?

    – Kusalananda
    5 hours ago











  • Relating unix.stackexchange.com/q/287077/117549

    – Jeff Schaller
    5 hours ago














  • 1





    Related, over at SO (for whatever reason): What are the real rules for linux usernames on CentOS 6 and RHEL 6?

    – Kusalananda
    5 hours ago











  • Relating unix.stackexchange.com/q/287077/117549

    – Jeff Schaller
    5 hours ago








1




1





Related, over at SO (for whatever reason): What are the real rules for linux usernames on CentOS 6 and RHEL 6?

– Kusalananda
5 hours ago





Related, over at SO (for whatever reason): What are the real rules for linux usernames on CentOS 6 and RHEL 6?

– Kusalananda
5 hours ago













Relating unix.stackexchange.com/q/287077/117549

– Jeff Schaller
5 hours ago





Relating unix.stackexchange.com/q/287077/117549

– Jeff Schaller
5 hours ago










1 Answer
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Note that useradd may be more restrictive than what is actually valid as a username. The rules as to what a valid username is may also change via PAM and nsswitch configuration settings.



The POSIX standard says that usernames must be from the "portable filename characterset" but the first character must not be a hyphen.



The portable filename character set are the characters A-Z a-z 0-9 . - _



Note this means that something like "1337" is a valid username according to this standard, which may cause issues elsewhere.



So, for safety, I would use a pattern such as [A-Za-z][A-Za-z0-9._-]+






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    Note that useradd may be more restrictive than what is actually valid as a username. The rules as to what a valid username is may also change via PAM and nsswitch configuration settings.



    The POSIX standard says that usernames must be from the "portable filename characterset" but the first character must not be a hyphen.



    The portable filename character set are the characters A-Z a-z 0-9 . - _



    Note this means that something like "1337" is a valid username according to this standard, which may cause issues elsewhere.



    So, for safety, I would use a pattern such as [A-Za-z][A-Za-z0-9._-]+






    share|improve this answer




























      0














      Note that useradd may be more restrictive than what is actually valid as a username. The rules as to what a valid username is may also change via PAM and nsswitch configuration settings.



      The POSIX standard says that usernames must be from the "portable filename characterset" but the first character must not be a hyphen.



      The portable filename character set are the characters A-Z a-z 0-9 . - _



      Note this means that something like "1337" is a valid username according to this standard, which may cause issues elsewhere.



      So, for safety, I would use a pattern such as [A-Za-z][A-Za-z0-9._-]+






      share|improve this answer


























        0












        0








        0







        Note that useradd may be more restrictive than what is actually valid as a username. The rules as to what a valid username is may also change via PAM and nsswitch configuration settings.



        The POSIX standard says that usernames must be from the "portable filename characterset" but the first character must not be a hyphen.



        The portable filename character set are the characters A-Z a-z 0-9 . - _



        Note this means that something like "1337" is a valid username according to this standard, which may cause issues elsewhere.



        So, for safety, I would use a pattern such as [A-Za-z][A-Za-z0-9._-]+






        share|improve this answer













        Note that useradd may be more restrictive than what is actually valid as a username. The rules as to what a valid username is may also change via PAM and nsswitch configuration settings.



        The POSIX standard says that usernames must be from the "portable filename characterset" but the first character must not be a hyphen.



        The portable filename character set are the characters A-Z a-z 0-9 . - _



        Note this means that something like "1337" is a valid username according to this standard, which may cause issues elsewhere.



        So, for safety, I would use a pattern such as [A-Za-z][A-Za-z0-9._-]+







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 4 hours ago









        Stephen HarrisStephen Harris

        26.8k35181




        26.8k35181






























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