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mystdeim
Asked: 2019-03-27 08:15:06 +0800 CST

Why I can't read file? [duplicate]

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Please look at output:

deploy@li445-201:~$ sudo ls -al /var/log/nginx/
total 152
drw-rw-r--  2 root     adm      4096 Mar 26 16:08 .
drwxrwxr-x 14 root     syslog   4096 Mar 26 06:25 ..
-rw-r--r--  1 root     root        0 Mar 26 16:08 access.log
-rwxrwxrwx  1 www-data adm    108849 Mar 26 06:10 access.log.1
-rw-rw-r--  1 www-data adm     14206 Mar 25 06:17 access.log.2.gz
-rw-rw-r--  1 www-data adm     14067 Mar 24 05:31 access.log.3.gz
-rw-r--r--  1 root     root        0 Mar 26 16:08 error.log
-rw-rw-r--  1 www-data adm      2522 Mar 24 17:13 error.log.1

I try to read log file by deploy user:

deploy@li445-201:~$ cat /var/log/nginx/access.log.1
cat: /var/log/nginx/access.log.1: Permission denied

Why I can't read log file? I've set even 777 permission on it

command-line permissions sudo ls cat

1 Answers

  1. The file's permissions show that any user should be able to read, write or execute the file. The directory in which this file is located, however, restricts this access.

    drw-rw-r--  2 root     adm      4096 Mar 26 16:08 .
# ^ /var/log/nginx 'bad'
drwxrwxr-x 14 root     syslog   4096 Mar 26 06:25 ..
# ^ /var/log 'good'

    In order for a user to be able to list the files in a directory, you need read and execute privileges. There is a good explanation of why you need the execute bit that you can read about here. You need to be able to access the inodes, which is where the requirement originates. I always thought you could read the file but not list the directory, but it seems you need the execute bit to read files in most situations.

    And this directory-based restriction goes all the way up to /. This is why a 777 file in your /home/$USER directory can't be accessed by another user, because your home directory has no read nor execute privileges for 'other'.

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