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Full Discussion: Check existence of a login
Top Forums UNIX for Advanced & Expert Users Check existence of a login Post 302172290 by xavier054 on Monday 3rd of March 2008 09:19:39 AM
Old 03-03-2008
MySQL

Quote:
Originally Posted by fpmurphy
No, in general, a shell does not know whether a particular user exists or not. The operating system may know that information.

As for tilde expansion, here is the relevant section from ksh93 s+.
Thanks, this answers my question. Furthermore I was wrong, and you are right: the shell knows only for users already logged at least once on the system. I could test getpwnam() on a set of PCs running Linux with PAM authentication, it failed for PAM logins of users that never logged on the machine. Same occurred with tidlde expansion.

BTW, I understand that getpwnam() manpage is confusing : it claims that /etc/passwd is parsed. But seen the output of last(1), and the outcome of my test, I understand it is rather /var/run/wtmp...

X.
 

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pwck(8) 						      System Manager's Manual							   pwck(8)

NAME
pwck, grpck - Checks the password and group files for inconsistencies SYNOPSIS
pwck [-admNs] [file] grpck [-mNp] [file] FLAGS
Causes both pwck and grpck to additionally check the NIS database entries using the same consistency tests. Users that are defined in the local password or group file without the "+" at the start of the name field are flagged as duplicate entries. pwck Inhibits the running of the /tcb/bin/authck -p command on a system running Enhanced Security. Prevents pwck from checking for the presence of the user's login directory. Directs pwck to check for mixed case usernames. Causes pwck to check for the presence of the optional shell field for each entry. grck If there are no members, causes grpck to display a message indicating the listed group has no members. Directs grpck to not check for a users' existence in the password database (local or NIS). DESCRIPTION
The pwck command scans the /etc/passwd file, or the named file, and writes to standard out any inconsistencies. The scan checks the number of fields, login name, user ID, group ID, and existence of a login directory and optional program name. The grpck command scans the /etc/group file, or the named file, and writes to standard out any inconsistencies. The scan checks the number of fields, group name, group ID, and whether all login names appear in the password file. EXAMPLES
To verify the password information in the /etc/passwd file for consistency, enter: pwck To verify the password information in the /etc/passwd file and the NIS database for consistency without checking each users login directory validity, enter: pwck -Nd To verify the group information in the /etc/group file and the NIS database for consistency, enter: grpck -N FILES
Specifies the command path Specifies the command path Contains user information Contains group information RELATED INFORMATION
Commands: adduser(8), authck(8), groups(1), passwd(1), vipw(8) Files: passwd(4), group(4), ypfiles(4) delim off pwck(8)
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