Description:
One of the most common and misleading error msgs in the MySQL project is,
"Can't find file: 'an_existent_file_path'"
I see so many times this msg confuses the users by telling them MySQL is looking for a file but fails to find it. However, in most cases, this is not true! In fact, the common causes are permission problems, i.e., MySQL does not have permissions to access the files.
Over the years, some of the log stmts are improved by giving the errono and then giving the error text. However, there're still many terrible msgs left, such as the following ones,
/* storage/ndb/src/kernel/blocks/dbdih/printFragfile.cpp */
228 if(stat(filename, &sbuf) != 0)
229 {
230 ndbout << "Could not find file: \"" << filename << "\"" << endl;
231 continue;
232 }
/* storage/ndb/src/kernel/blocks/dbdih/printSysfile.cpp */
145 if(stat(filename, &sbuf) != 0)
146 {
147 ndbout << "Could not find file: \"" << filename << "\"" << endl;
148 continue;
149 }
/* storage/ndb/src/kernel/blocks/print_file.cpp */
74 if(stat(filename, &sbuf) != 0)
75 {
76 ndbout << "Could not find file: \"" << filename << "\"" << endl;
77 continue;
78 }
/* storage/ndb/src/common/mgmcommon/ConfigRetriever.cpp */
193 if (access(filename, F_OK))
194 {
195 BaseString err;
196 err.assfmt("Could not find file: '%s'", filename);
197 setError(CR_ERROR, err);
198 return 0;
199 }
Seriously, why can't we just tell users that MySQL encounters error when stat/access the file? There're really too many reasons to fail stat()/access() besides "file cannot be found"... In my experience, permission issues are the most common ones.
How to repeat:
To repeat, simply chmod a system file in the datadir, e.g., plugin.db, and then start mysqld, you will see something like,
"bin/mysqld: Can't find file: './mysql/db.frm' (errno: 13 - Permission denied)"
This one is printed when an open() call fails in open_table_def(),
748 if (length == share->normalized_path.length ||
749 ((file= mysql_file_open(key_file_frm,
750 path, O_RDONLY | O_SHARE, MYF(0))) < 0))
751 goto err_not_open;
...
833 err_not_open:
834 if (error && !error_given)
835 {
836 share->error= error;
837 open_table_error(share, error, (share->open_errno= my_errno()), 0);
838 }
Suggested fix:
In error logs, just precisely tell which file operation (e.g., open, access, stat) fails, rather than tell users something like "can't find the file" etc. I did see people use strace to figure out what was failed inside the box.
Description: One of the most common and misleading error msgs in the MySQL project is, "Can't find file: 'an_existent_file_path'" I see so many times this msg confuses the users by telling them MySQL is looking for a file but fails to find it. However, in most cases, this is not true! In fact, the common causes are permission problems, i.e., MySQL does not have permissions to access the files. Over the years, some of the log stmts are improved by giving the errono and then giving the error text. However, there're still many terrible msgs left, such as the following ones, /* storage/ndb/src/kernel/blocks/dbdih/printFragfile.cpp */ 228 if(stat(filename, &sbuf) != 0) 229 { 230 ndbout << "Could not find file: \"" << filename << "\"" << endl; 231 continue; 232 } /* storage/ndb/src/kernel/blocks/dbdih/printSysfile.cpp */ 145 if(stat(filename, &sbuf) != 0) 146 { 147 ndbout << "Could not find file: \"" << filename << "\"" << endl; 148 continue; 149 } /* storage/ndb/src/kernel/blocks/print_file.cpp */ 74 if(stat(filename, &sbuf) != 0) 75 { 76 ndbout << "Could not find file: \"" << filename << "\"" << endl; 77 continue; 78 } /* storage/ndb/src/common/mgmcommon/ConfigRetriever.cpp */ 193 if (access(filename, F_OK)) 194 { 195 BaseString err; 196 err.assfmt("Could not find file: '%s'", filename); 197 setError(CR_ERROR, err); 198 return 0; 199 } Seriously, why can't we just tell users that MySQL encounters error when stat/access the file? There're really too many reasons to fail stat()/access() besides "file cannot be found"... In my experience, permission issues are the most common ones. How to repeat: To repeat, simply chmod a system file in the datadir, e.g., plugin.db, and then start mysqld, you will see something like, "bin/mysqld: Can't find file: './mysql/db.frm' (errno: 13 - Permission denied)" This one is printed when an open() call fails in open_table_def(), 748 if (length == share->normalized_path.length || 749 ((file= mysql_file_open(key_file_frm, 750 path, O_RDONLY | O_SHARE, MYF(0))) < 0)) 751 goto err_not_open; ... 833 err_not_open: 834 if (error && !error_given) 835 { 836 share->error= error; 837 open_table_error(share, error, (share->open_errno= my_errno()), 0); 838 } Suggested fix: In error logs, just precisely tell which file operation (e.g., open, access, stat) fails, rather than tell users something like "can't find the file" etc. I did see people use strace to figure out what was failed inside the box.