Why would /etc/passwd be used every time someone executes `ls -l` command?
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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 anls -lcommand.
ls passwd
edited Mar 8 at 5:12
Olorin
3,9581723
asked Mar 8 at 4:07
RickRick
287310
add a comment |
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 anls -lcommand.
ls passwd
edited Mar 8 at 5:12
Olorin
3,9581723
asked Mar 8 at 4:07
RickRick
287310
3
FYI I trystrace ls -llater on, I see aopenat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4statement.
– Rick
Mar 8 at 6:47
6
Of course, reality is more complex nowadays. It's not/etc/passwdon the BSDs. An activenscdwill change things; as will the NSS. So note that this question is based upon a 7th Edition worldview.
– JdeBP
Mar 8 at 7:55
4
@JdeBP Ancient Programming in the Unix Environment, then?
– Andrew Henle
Mar 8 at 13:22
@JdeBP It isn't? I wa surprised when you said that because I'd think that a lot of programs (scripts and binaries) would break which rely (perhaps wrongly, but still) on the presence of /etc/passwd.
– Peter A. Schneider
Mar 9 at 12:02
It isn't, as reading that manual page properly, including its FILES section, will reveal. (-:
– JdeBP
Mar 11 at 12:39
add a comment |
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 anls -lcommand.
ls passwd
edited Mar 8 at 5:12
Olorin
3,9581723
asked Mar 8 at 4:07
RickRick
287310
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 anls -lcommand.
ls passwd
ls passwd
edited Mar 8 at 5:12
Olorin
3,9581723
asked Mar 8 at 4:07
RickRick
287310
edited Mar 8 at 5:12
Olorin
3,9581723
asked Mar 8 at 4:07
RickRick
287310
edited Mar 8 at 5:12
Olorin
3,9581723
edited Mar 8 at 5:12
Olorin
3,9581723
edited Mar 8 at 5:12
Olorin
3,9581723
3,9581723
asked Mar 8 at 4:07
RickRick
287310
asked Mar 8 at 4:07
RickRick
287310
asked Mar 8 at 4:07
RickRick
287310
287310
3
FYI I trystrace ls -llater on, I see aopenat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4statement.
– Rick
Mar 8 at 6:47
6
Of course, reality is more complex nowadays. It's not/etc/passwdon the BSDs. An activenscdwill change things; as will the NSS. So note that this question is based upon a 7th Edition worldview.
– JdeBP
Mar 8 at 7:55
4
@JdeBP Ancient Programming in the Unix Environment, then?
– Andrew Henle
Mar 8 at 13:22
@JdeBP It isn't? I wa surprised when you said that because I'd think that a lot of programs (scripts and binaries) would break which rely (perhaps wrongly, but still) on the presence of /etc/passwd.
– Peter A. Schneider
Mar 9 at 12:02
It isn't, as reading that manual page properly, including its FILES section, will reveal. (-:
– JdeBP
Mar 11 at 12:39
add a comment |
3
FYI I trystrace ls -llater on, I see aopenat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4statement.
– Rick
Mar 8 at 6:47
6
Of course, reality is more complex nowadays. It's not/etc/passwdon the BSDs. An activenscdwill change things; as will the NSS. So note that this question is based upon a 7th Edition worldview.
– JdeBP
Mar 8 at 7:55
4
@JdeBP Ancient Programming in the Unix Environment, then?
– Andrew Henle
Mar 8 at 13:22
@JdeBP It isn't? I wa surprised when you said that because I'd think that a lot of programs (scripts and binaries) would break which rely (perhaps wrongly, but still) on the presence of /etc/passwd.
– Peter A. Schneider
Mar 9 at 12:02
It isn't, as reading that manual page properly, including its FILES section, will reveal. (-:
– JdeBP
Mar 11 at 12:39
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
Mar 8 at 6:47
FYI I try
strace ls -l later on, I see a openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4 statement.– Rick
Mar 8 at 6:47
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
Mar 8 at 7:55
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
Mar 8 at 7:55
4
4
@JdeBP Ancient Programming in the Unix Environment, then?
– Andrew Henle
Mar 8 at 13:22
@JdeBP Ancient Programming in the Unix Environment, then?
– Andrew Henle
Mar 8 at 13:22
@JdeBP It isn't? I wa surprised when you said that because I'd think that a lot of programs (scripts and binaries) would break which rely (perhaps wrongly, but still) on the presence of /etc/passwd.
– Peter A. Schneider
Mar 9 at 12:02
@JdeBP It isn't? I wa surprised when you said that because I'd think that a lot of programs (scripts and binaries) would break which rely (perhaps wrongly, but still) on the presence of /etc/passwd.
– Peter A. Schneider
Mar 9 at 12:02
It isn't, as reading that manual page properly, including its FILES section, will reveal. (-:
– JdeBP
Mar 11 at 12:39
It isn't, as reading that manual page properly, including its FILES section, will reveal. (-:
– JdeBP
Mar 11 at 12:39
add a comment |
1 Answer
1
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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
answered Mar 8 at 4:48
igaligal
6,1411638
16
To complement the answer: POSIX specifies option-nforls. This prevents translation of UIDs and GIDs to usernames and group names. I have testedls -nwith GNU core utils'lsand the option prevented accessing both/etc/passwdand/etc/groupas expected.
– pabouk
Mar 8 at 8:54
add a comment |
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1 Answer
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active
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1 Answer
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active
oldest
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active
oldest
votes
active
oldest
votes
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
answered Mar 8 at 4:48
igaligal
6,1411638
16
To complement the answer: POSIX specifies option-nforls. This prevents translation of UIDs and GIDs to usernames and group names. I have testedls -nwith GNU core utils'lsand the option prevented accessing both/etc/passwdand/etc/groupas expected.
– pabouk
Mar 8 at 8:54
add a comment |
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
answered Mar 8 at 4:48
igaligal
6,1411638
16
To complement the answer: POSIX specifies option-nforls. This prevents translation of UIDs and GIDs to usernames and group names. I have testedls -nwith GNU core utils'lsand the option prevented accessing both/etc/passwdand/etc/groupas expected.
– pabouk
Mar 8 at 8:54
add a comment |
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
answered Mar 8 at 4:48
igaligal
6,1411638
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
answered Mar 8 at 4:48
igaligal
6,1411638
edited Mar 8 at 4:54
answered Mar 8 at 4:48
igaligal
6,1411638
answered Mar 8 at 4:48
igaligal
6,1411638
answered Mar 8 at 4:48
igaligal
6,1411638
6,1411638
16
To complement the answer: POSIX specifies option-nforls. This prevents translation of UIDs and GIDs to usernames and group names. I have testedls -nwith GNU core utils'lsand the option prevented accessing both/etc/passwdand/etc/groupas expected.
– pabouk
Mar 8 at 8:54
add a comment |
16
To complement the answer: POSIX specifies option-nforls. This prevents translation of UIDs and GIDs to usernames and group names. I have testedls -nwith GNU core utils'lsand the option prevented accessing both/etc/passwdand/etc/groupas expected.
– pabouk
Mar 8 at 8:54
16
16
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
Mar 8 at 8:54
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
Mar 8 at 8:54
add a comment |
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3
FYI I try
strace ls -llater on, I see aopenat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4statement.– Rick
Mar 8 at 6:47
6
Of course, reality is more complex nowadays. It's not
/etc/passwdon the BSDs. An activenscdwill change things; as will the NSS. So note that this question is based upon a 7th Edition worldview.– JdeBP
Mar 8 at 7:55
4
@JdeBP Ancient Programming in the Unix Environment, then?
– Andrew Henle
Mar 8 at 13:22
@JdeBP It isn't? I wa surprised when you said that because I'd think that a lot of programs (scripts and binaries) would break which rely (perhaps wrongly, but still) on the presence of /etc/passwd.
– Peter A. Schneider
Mar 9 at 12:02
It isn't, as reading that manual page properly, including its FILES section, will reveal. (-:
– JdeBP
Mar 11 at 12:39