Why would /etc/passwd be used every time someone executes `ls -l` command?












18















Read from APUE, just feel curious:




The password file is used every time a user logs in to a
UNIX system and every time someone executes an ls -l command.







ls passwd







share|improve this question




















  • 3





    FYI I try strace ls -l later on, I see a openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4 statement.

    – Rick
    22 hours ago








  • 6





    Of course, reality is more complex nowadays. It's not /etc/passwd on the BSDs. An active nscd will change things; as will the NSS. So note that this question is based upon a 7th Edition worldview.

    – JdeBP
    21 hours ago






  • 4





    @JdeBP Ancient Programming in the Unix Environment, then?

    – Andrew Henle
    15 hours ago
















18















Read from APUE, just feel curious:




The password file is used every time a user logs in to a
UNIX system and every time someone executes an ls -l command.







ls passwd







share|improve this question




















  • 3





    FYI I try strace ls -l later on, I see a openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4 statement.

    – Rick
    22 hours ago








  • 6





    Of course, reality is more complex nowadays. It's not /etc/passwd on the BSDs. An active nscd will change things; as will the NSS. So note that this question is based upon a 7th Edition worldview.

    – JdeBP
    21 hours ago






  • 4





    @JdeBP Ancient Programming in the Unix Environment, then?

    – Andrew Henle
    15 hours ago














18












18








18


1






Read from APUE, just feel curious:




The password file is used every time a user logs in to a
UNIX system and every time someone executes an ls -l command.







ls passwd







share|improve this question
















Read from APUE, just feel curious:




The password file is used every time a user logs in to a
UNIX system and every time someone executes an ls -l command.







ls passwd




ls passwd






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited yesterday









Olorin

3,8781721




3,8781721










asked yesterday









RickRick

20317




20317








  • 3





    FYI I try strace ls -l later on, I see a openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4 statement.

    – Rick
    22 hours ago








  • 6





    Of course, reality is more complex nowadays. It's not /etc/passwd on the BSDs. An active nscd will change things; as will the NSS. So note that this question is based upon a 7th Edition worldview.

    – JdeBP
    21 hours ago






  • 4





    @JdeBP Ancient Programming in the Unix Environment, then?

    – Andrew Henle
    15 hours ago














  • 3





    FYI I try strace ls -l later on, I see a openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4 statement.

    – Rick
    22 hours ago








  • 6





    Of course, reality is more complex nowadays. It's not /etc/passwd on the BSDs. An active nscd will change things; as will the NSS. So note that this question is based upon a 7th Edition worldview.

    – JdeBP
    21 hours ago






  • 4





    @JdeBP Ancient Programming in the Unix Environment, then?

    – Andrew Henle
    15 hours ago








3




3





FYI I try strace ls -l later on, I see a openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4 statement.

– Rick
22 hours ago







FYI I try strace ls -l later on, I see a openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4 statement.

– Rick
22 hours ago






6




6





Of course, reality is more complex nowadays. It's not /etc/passwd on the BSDs. An active nscd will change things; as will the NSS. So note that this question is based upon a 7th Edition worldview.

– JdeBP
21 hours ago





Of course, reality is more complex nowadays. It's not /etc/passwd on the BSDs. An active nscd will change things; as will the NSS. So note that this question is based upon a 7th Edition worldview.

– JdeBP
21 hours ago




4




4





@JdeBP Ancient Programming in the Unix Environment, then?

– Andrew Henle
15 hours ago





@JdeBP Ancient Programming in the Unix Environment, then?

– Andrew Henle
15 hours ago










1 Answer
1






active

oldest

votes


















31














The file-system directly associates the numerical UID (User ID) and GID (Group ID) values with the file, not the user name and group name (which are strings). So the ls -l command (and any other command that displays the user and group owner of a file) need to get the user and group names from somewhere. The /etc/passwd file is one such source (probably the original and most common source). The manual bears this out - from PASSWD (5) (i.e. the man page for the /etc/passwd file):




many utilities, like ls(1) use it to map user IDs to usernames







share|improve this answer





















  • 10





    To complement the answer: POSIX specifies option -n for ls. This prevents translation of UIDs and GIDs to usernames and group names. I have tested ls -n with GNU core utils' ls and the option prevented accessing both /etc/passwd and /etc/group as expected.

    – pabouk
    20 hours ago











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1 Answer
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active

oldest

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1 Answer
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active

oldest

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active

oldest

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active

oldest

votes









31














The file-system directly associates the numerical UID (User ID) and GID (Group ID) values with the file, not the user name and group name (which are strings). So the ls -l command (and any other command that displays the user and group owner of a file) need to get the user and group names from somewhere. The /etc/passwd file is one such source (probably the original and most common source). The manual bears this out - from PASSWD (5) (i.e. the man page for the /etc/passwd file):




many utilities, like ls(1) use it to map user IDs to usernames







share|improve this answer





















  • 10





    To complement the answer: POSIX specifies option -n for ls. This prevents translation of UIDs and GIDs to usernames and group names. I have tested ls -n with GNU core utils' ls and the option prevented accessing both /etc/passwd and /etc/group as expected.

    – pabouk
    20 hours ago
















31














The file-system directly associates the numerical UID (User ID) and GID (Group ID) values with the file, not the user name and group name (which are strings). So the ls -l command (and any other command that displays the user and group owner of a file) need to get the user and group names from somewhere. The /etc/passwd file is one such source (probably the original and most common source). The manual bears this out - from PASSWD (5) (i.e. the man page for the /etc/passwd file):




many utilities, like ls(1) use it to map user IDs to usernames







share|improve this answer





















  • 10





    To complement the answer: POSIX specifies option -n for ls. This prevents translation of UIDs and GIDs to usernames and group names. I have tested ls -n with GNU core utils' ls and the option prevented accessing both /etc/passwd and /etc/group as expected.

    – pabouk
    20 hours ago














31












31








31







The file-system directly associates the numerical UID (User ID) and GID (Group ID) values with the file, not the user name and group name (which are strings). So the ls -l command (and any other command that displays the user and group owner of a file) need to get the user and group names from somewhere. The /etc/passwd file is one such source (probably the original and most common source). The manual bears this out - from PASSWD (5) (i.e. the man page for the /etc/passwd file):




many utilities, like ls(1) use it to map user IDs to usernames







share|improve this answer















The file-system directly associates the numerical UID (User ID) and GID (Group ID) values with the file, not the user name and group name (which are strings). So the ls -l command (and any other command that displays the user and group owner of a file) need to get the user and group names from somewhere. The /etc/passwd file is one such source (probably the original and most common source). The manual bears this out - from PASSWD (5) (i.e. the man page for the /etc/passwd file):




many utilities, like ls(1) use it to map user IDs to usernames








share|improve this answer














share|improve this answer



share|improve this answer








edited yesterday

























answered yesterday









igaligal

5,5511435




5,5511435








  • 10





    To complement the answer: POSIX specifies option -n for ls. This prevents translation of UIDs and GIDs to usernames and group names. I have tested ls -n with GNU core utils' ls and the option prevented accessing both /etc/passwd and /etc/group as expected.

    – pabouk
    20 hours ago














  • 10





    To complement the answer: POSIX specifies option -n for ls. This prevents translation of UIDs and GIDs to usernames and group names. I have tested ls -n with GNU core utils' ls and the option prevented accessing both /etc/passwd and /etc/group as expected.

    – pabouk
    20 hours ago








10




10





To complement the answer: POSIX specifies option -n for ls. This prevents translation of UIDs and GIDs to usernames and group names. I have tested ls -n with GNU core utils' ls and the option prevented accessing both /etc/passwd and /etc/group as expected.

– pabouk
20 hours ago





To complement the answer: POSIX specifies option -n for ls. This prevents translation of UIDs and GIDs to usernames and group names. I have tested ls -n with GNU core utils' ls and the option prevented accessing both /etc/passwd and /etc/group as expected.

– pabouk
20 hours ago


















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