: Apache 2.4: Symlinks to CIFS mount are served, but not seen by PHP or mod_autoindex I'm trying to run the Piwigo image gallery/DAM on a Raspberry Pi via Arch Linux ARM with Apache 2.4 and

I'm trying to run the Piwigo image gallery/DAM on a Raspberry Pi via Arch Linux ARM with Apache 2.4 and PHP7. Piwigo is running happily. For a chain of reasons outside the scope of this question, my goal is to leave the tens of thousands of image files on a Windows machine, share them up through CIFS and symlink them into Piwigo's FTP/synchronization directory. Symlinking files into Piwigo is an everyday practice, recommended by its documentation and developers in its forums.

My files are mounted with options making them owned by Apache's user. All files, including symlinks into the CIFS share, are served OK by Apache if their URLs are typed in. This isn't a permissions issue, or at least not a simple one. The problem is that symlinks into the CIFS share are not listed or synchronized by Piwigo's PHP. Symlinks to the local filesystem are synchronized OK. Although autoindexes aren't involved in my goal, I think it's a clue that the same exact rules apply to indexes generated by mod_autoindex.

Setting up a test case:

[alarm@alarmpi familytreetest]$ sudo -u http -s
[http@alarmpi ~]$ mkdir /mnt/localfam
[http@alarmpi ~]$ cp /mnt/familytreetest/Bulk Uploads/1977 Andrews/1977 Andrews_1.jpg /mnt/localfam/
[http@alarmpi ~]$ ln -s /mnt/familytreetest/Bulk Uploads/1977 Andrews/1977 Andrews_1.jpg /srv/http/piwigo/galleries/family/CIFSlink.jpg
[http@alarmpi ~]$ ln -s /mnt/localfam/ /srv/http/piwigo/galleries/family/Locallink.jpg
[http@alarmpi ~]$ cp /mnt/localfam/1977 Andrews_1.jpg piwigo/galleries/family/1977_Andrews_1.jpg

The name change in copying the file into Piwigo is intentional; Piwigo can't handle spaces in this particular function.

When I was recording and editing all this output, I failed to think about paths with spaces. I just tested; symlinks to paths on the local filesystem which include spaces are both synchronized by Piwigo and listed by mod_autoindex. I'd prefer not to spend more hours redoing all the listings to convince people on this one matter, but will if necessary.

[http@alarmpi ~]$ ls -l piwigo/galleries/family/
total 240
-rwxr-xr-x 1 http http 237934 Dec 23 17:43 1977_Andrews_1.jpg
lrwxrwxrwx 1 http http 64 Dec 23 17:28 CIFSlink.jpg -> /mnt/familytreetest/Bulk Uploads/1977 Andrews/1977 Andrews_1.jpg
lrwxrwxrwx 1 http http 32 Dec 23 17:42 Locallink.jpg -> /mnt/localfam/1977 Andrews_1.jpg

At this point I run Piwigo's synchronization tool. I get two images added to my database. CIFSlink.jpg is left out. If I now type in any of these files' URLs in any browser on any machine on my network, I get the picture on screen OK.

[http@alarmpi ~]$ curl -I 192.168.0.100/piwigo/galleries/family/CIFSlink.jpg
HTTP/1.1 200 OK
Date: Sat, 23 Dec 2017 23:35:49 GMT
Server: Apache/2.4.25 (Unix) PHP/7.1.5
Last-Modified: Mon, 24 Jul 2017 18:00:52 GMT
ETag: "3a16e-55513feda1d00"
Accept-Ranges: bytes
Content-Length: 237934
Content-Type: image/jpeg

I copy the sync directory out to Apache's DocumentRoot (which is also user http's home directory) so I can browse to it with mod_autoindex.

[http@alarmpi ~]$ cp -r piwigo/galleries/family/ /srv/http/

Here too CIFSlink.jpg is left out of the listing.

[http@alarmpi ~]$ curl 192.168.0.100/family/
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<html>
<head>
<title>Index of /family</title>
</head>
<body>
<h1>Index of /family</h1>
<table>
<tr><th valign="top"><img src="/icons/blank.gif" alt="[ICO]"></th><th><a href="?C=N;O=D">Name</a></th><th><a href="?C=M;O=A">Last modified</a></th><th><a href="?C=S;O=A">Size</a></th><th><a href="?C=D;O=A">Description</a></th></tr>
<tr><th colspan="5"><hr></th></tr>
<tr><td valign="top"><img src="/icons/back.gif" alt="[PARENTDIR]"></td><td><a href="/">Parent Directory</a> </td><td> </td><td align="right"> - </td><td> </td></tr>
<tr><td valign="top"><img src="/icons/image2.gif" alt="[IMG]"></td><td><a href="1977_Andrews_1.jpg">1977_Andrews_1.jpg</a> </td><td align="right">2017-12-23 18:49 </td><td align="right">232K</td><td> </td></tr>
<tr><td valign="top"><img src="/icons/image2.gif" alt="[IMG]"></td><td><a href="Locallink.jpg">Locallink.jpg</a> </td><td align="right">2017-12-23 17:22 </td><td align="right">232K</td><td> </td></tr>
<tr><th colspan="5"><hr></th></tr>
</table>
</body></html>

Here too, the file is accessible just fine by Apache through its URL.

[http@alarmpi ~]$ curl -I 192.168.0.100/family/CIFSlink.jpg
HTTP/1.1 200 OK
Date: Sat, 23 Dec 2017 23:58:29 GMT
Server: Apache/2.4.25 (Unix) PHP/7.1.5
Last-Modified: Mon, 24 Jul 2017 18:00:52 GMT
ETag: "3a16e-55513feda1d00"
Accept-Ranges: bytes
Content-Length: 237934
Content-Type: image/jpeg

Apache's access and error logs removed to get under 30K chars. Didn't show anything seeming relevant.

EDIT: If I mount the CIFS share directly to where I'm putting the symlinks, files are not seen by the PHP application, even if they have no illegal characters, but are included in indexes from mod_autoindex.

My httpd.conf, passed through awk to strip comments and blank lines:

[alarm@alarmpi familytreetest]$ sudo awk '!/^ *#/ && NF' /etc/httpd/conf/httpd.conf
ServerRoot "/etc/httpd"
Listen 80
LoadModule authn_file_module modules/mod_authn_file.so
LoadModule authn_core_module modules/mod_authn_core.so
LoadModule authz_host_module modules/mod_authz_host.so
LoadModule authz_groupfile_module modules/mod_authz_groupfile.so
LoadModule authz_user_module modules/mod_authz_user.so
LoadModule authz_core_module modules/mod_authz_core.so
LoadModule access_compat_module modules/mod_access_compat.so
LoadModule auth_basic_module modules/mod_auth_basic.so
LoadModule reqtimeout_module modules/mod_reqtimeout.so
LoadModule include_module modules/mod_include.so
LoadModule filter_module modules/mod_filter.so
LoadModule mime_module modules/mod_mime.so
LoadModule log_config_module modules/mod_log_config.so
LoadModule env_module modules/mod_env.so
LoadModule headers_module modules/mod_headers.so
LoadModule unique_id_module modules/mod_unique_id.so
LoadModule setenvif_module modules/mod_setenvif.so
LoadModule version_module modules/mod_version.so
LoadModule slotmem_shm_module modules/mod_slotmem_shm.so
LoadModule mpm_prefork_module modules/mod_mpm_prefork.so
LoadModule unixd_module modules/mod_unixd.so
LoadModule status_module modules/mod_status.so
LoadModule autoindex_module modules/mod_autoindex.so
<IfModule !mpm_prefork_module>
#LoadModule cgid_module modules/mod_cgid.so
</IfModule>
<IfModule mpm_prefork_module>
#LoadModule cgi_module modules/mod_cgi.so
</IfModule>
LoadModule negotiation_module modules/mod_negotiation.so
LoadModule dir_module modules/mod_dir.so
LoadModule userdir_module modules/mod_userdir.so
LoadModule alias_module modules/mod_alias.so
LoadModule php7_module modules/libphp7.so
<FilesMatch .php$>
SetHandler application/x-httpd-php
</FilesMatch>
<IfModule unixd_module>
User http
Group http
</IfModule>
ServerAdmin you@example.com
<Directory />
AllowOverride none
Require all denied
</Directory>
DocumentRoot "/srv/http"
<Directory "/srv/http">
Options +Indexes +FollowSymLinks
AllowOverride None
Require all granted
</Directory>
<IfModule dir_module>
DirectoryIndex index.html
</IfModule>
<Files ".ht*">
Require all denied
</Files>
ErrorLog "/var/log/httpd/error_log"
LogLevel warn
<IfModule log_config_module>
LogFormat "%h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-Agent}i"" combined
LogFormat "%h %l %u %t "%r" %>s %b" common
<IfModule logio_module>
LogFormat "%h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-Agent}i" %I %O" combinedio
</IfModule>
CustomLog "/var/log/httpd/access_log" common
</IfModule>
<IfModule alias_module>
ScriptAlias /cgi-bin/ "/srv/http/cgi-bin/"
</IfModule>
<IfModule cgid_module>
</IfModule>
<Directory "/srv/http/cgi-bin">
AllowOverride None
Options None
Require all granted
</Directory>
<IfModule headers_module>
RequestHeader unset Proxy early
</IfModule>
<IfModule mime_module>
TypesConfig conf/mime.types
AddType application/x-compress .Z
AddType application/x-gzip .gz .tgz
</IfModule>
Include conf/extra/httpd-mpm.conf
Include conf/extra/httpd-multilang-errordoc.conf
Include conf/extra/httpd-autoindex.conf
Include conf/extra/httpd-languages.conf
Include conf/extra/httpd-userdir.conf
Include conf/extra/httpd-default.conf
Include conf/extra/phpmyadmin.conf
<IfModule proxy_html_module>
Include conf/extra/proxy-html.conf
</IfModule>
Include conf/extra/php7_module.conf
<IfModule ssl_module>
SSLRandomSeed startup builtin
SSLRandomSeed connect builtin
</IfModule>

I haven't changed httpd.conf in two weeks and have restarted it a dozen times to be sure the server's up to date on its configuration.

I had my other Apache conf files, but they put me over 30K characters. Available upon request by editing other stuff out.

SELinux isn't officially supported on Arch Linux, let alone ALARM. I have not gone through the super-hairy process to install the half-working version you can put in. In any case, its main diagnostic command says it's not here and can't be screwing stuff up.

[alarm@alarmpi ~]$ sestatus
-bash: sestatus: command not found

The final thing I can think of is to throw you an strace of Apache trying to scan these files. First, Piwigo's worker doing a synchronization. Actual mention of the files it's supposed to see at lines 57-61 and again at 81-84. I notice that in the first block it scans the first two files, then hits the directory again, and only then hits CIFSlink. In the second block, it's potentially interesting that CIFSlink and only CIFSlink is hit twice. Everything's still return status 0, though. I've gone back and confirmed that the final action on files at 158-166 happens even when I perform no action but a synchronization before ctrl-C terminating Apache. That sole call of readlink() at 162 remains the only call even if two local symlinks are successfully synchronized.

[alarm@alarmpi ~]$ nl phpstrace.txt | less
(snip)
43 20559 send(10, "E3nSELECT IF(MAX(id)+1 IS NUL"..., 73, MSG_DONTWAIT) = 73
44 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
45 20559 recv(10, "1101923def#IF(MAX(id)+1 IS"..., 1479, MSG_DONTWAIT) = 90
46 20559 gettimeofday({tv_sec=1514078472, tv_usec=648129}, NULL) = 0
47 20559 stat64("./galleries", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
48 20559 open("./galleries", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 11
49 20559 fstat64(11, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
50 20559 getdents(11, /* 4 entries */, 32768) = 76
51 20559 stat64("./galleries/.", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
52 20559 stat64("./galleries/..", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
53 20559 stat64("./galleries/family", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
54 20559 open("./galleries/family", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 12
55 20559 fstat64(12, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
56 20559 getdents(12, /* 5 entries */, 32768) = 116
57 20559 stat64("./galleries/family/1977_Andrews_1.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
58 20559 stat64("./galleries/family/Locallink.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
59 20559 stat64("./galleries/family/.", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
60 20559 stat64("./galleries/family/CIFSlink.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
61 20559 stat64("./galleries/family/..", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
62 20559 getdents(12, /* 0 entries */, 32768) = 0
63 20559 close(12) = 0
64 20559 stat64("./galleries/index.php", {st_mode=S_IFREG|0644, st_size=1765, ...}) = 0
65 20559 getdents(11, /* 0 entries */, 32768) = 0
66 20559 close(11) = 0
67 20559 gettimeofday({tv_sec=1514078472, tv_usec=671461}, NULL) = 0
68 20559 gettimeofday({tv_sec=1514078472, tv_usec=672515}, NULL) = 0
69 20559 stat64("./galleries", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
70 20559 open("./galleries", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 11
71 20559 fstat64(11, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
72 20559 getdents(11, /* 4 entries */, 32768) = 76
73 20559 stat64("./galleries/family", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
74 20559 stat64("./galleries/index.php", {st_mode=S_IFREG|0644, st_size=1765, ...}) = 0
75 20559 getdents(11, /* 0 entries */, 32768) = 0
76 20559 close(11) = 0
77 20559 stat64("./galleries/family", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
78 20559 open("./galleries/family", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 11
79 20559 fstat64(11, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
80 20559 getdents(11, /* 5 entries */, 32768) = 116
81 20559 stat64("./galleries/family/1977_Andrews_1.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
82 20559 stat64("./galleries/family/Locallink.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
83 20559 stat64("./galleries/family/CIFSlink.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
84 20559 stat64("./galleries/family/CIFSlink.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
85 20559 getdents(11, /* 0 entries */, 32768) = 0
86 20559 close(11) = 0
87 20559 gettimeofday({tv_sec=1514078472, tv_usec=685288}, NULL) = 0
88 20559 gettimeofday({tv_sec=1514078472, tv_usec=686100}, NULL) = 0
89 20559 send(10, "I3nSELECT id, pathn FROM piw"..., 77, MSG_DONTWAIT) = 77
90 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
91 20559 recv(10, "112=23deftpiwigopixrpiwigo_i"..., 1389, MSG_DONTWAIT) = 240
92 20559 gettimeofday({tv_sec=1514078472, tv_usec=691698}, NULL) = 0
93 20559 gettimeofday({tv_sec=1514078472, tv_usec=692510}, NULL) = 0
94 20559 send(10, "A3nSELECT IF(MAX(id)+1 IS NUL"..., 69, MSG_DONTWAIT) = 69
95 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
96 20559 recv(10, "1101923def#IF(MAX(id)+1 IS"..., 1149, MSG_DONTWAIT) = 90
97 20559 gettimeofday({tv_sec=1514078472, tv_usec=697001}, NULL) = 0
98 20559 gettimeofday({tv_sec=1514078472, tv_usec=697784}, NULL) = 0
99 20559 gettimeofday({tv_sec=1514078472, tv_usec=698459}, NULL) = 0
100 20559 gettimeofday({tv_sec=1514078472, tv_usec=699212}, NULL) = 0
101 20559 gettimeofday({tv_sec=1514078472, tv_usec=699768}, NULL) = 0
102 20559 send(10, "3143nSELECT DISTINCT c.idn FRO"..., 208, MSG_DONTWAIT) = 208
103 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
104 20559 recv(10, "1101523deftpiwigopix1c21piwigo"..., 1059, MSG_DONTWAIT) = 80
105 20559 gettimeofday({tv_sec=1514078472, tv_usec=706517}, NULL) = 0
106 20559 gettimeofday({tv_sec=1514078472, tv_usec=707219}, NULL) = 0
107 20559 send(10, "2363nSELECT DISTINCT idn FROM "..., 162, MSG_DONTWAIT) = 162
108 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
109 20559 recv(10, "111E23deftpiwigopix21piwigo_c"..., 979, MSG_DONTWAIT) = 96
110 20559 gettimeofday({tv_sec=1514078472, tv_usec=713776}, NULL) = 0
111 20559 gettimeofday({tv_sec=1514078472, tv_usec=714489}, NULL) = 0
112 20559 gettimeofday({tv_sec=1514078472, tv_usec=715212}, NULL) = 0
113 20559 gettimeofday({tv_sec=1514078472, tv_usec=715798}, NULL) = 0
114 20559 send(10, "p3nSELECT id, id_uppercat, up"..., 116, MSG_DONTWAIT) = 116
115 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
116 20559 recv(10, "115E23deftpiwigopix21piwigo_c"..., 883, MSG_DONTWAIT) = 468
117 20559 gettimeofday({tv_sec=1514078472, tv_usec=721655}, NULL) = 0
118 20559 gettimeofday({tv_sec=1514078472, tv_usec=723454}, NULL) = 0
119 20559 gettimeofday({tv_sec=1514078472, tv_usec=724212}, NULL) = 0
120 20559 gettimeofday({tv_sec=1514078472, tv_usec=724792}, NULL) = 0
121 20559 send(10, "R3nSELECT idn FROM piwigo_ca"..., 86, MSG_DONTWAIT) = 86
122 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
123 20559 recv(10, "111E23deftpiwigopix21piwigo_c"..., 415, MSG_DONTWAIT) = 102
124 20559 gettimeofday({tv_sec=1514078472, tv_usec=730105}, NULL) = 0
125 20559 gettimeofday({tv_sec=1514078472, tv_usec=730977}, NULL) = 0
126 20559 send(10, "_3nSELECT id, path, represent"..., 99, MSG_DONTWAIT) = 99
127 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
128 20559 recv(10, "113=23deftpiwigopixrpiwigo_i"..., 313, MSG_DONTWAIT) = 313
129 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
130 20559 recv(10, "77_Andrews_1.jpg3735103762", 2500, MSG_DONTWAIT) = 26
131 20559 gettimeofday({tv_sec=1514078472, tv_usec=737467}, NULL) = 0
132 20559 gettimeofday({tv_sec=1514078472, tv_usec=738418}, NULL) = 0
133 20559 gettimeofday({tv_sec=1514078472, tv_usec=739147}, NULL) = 0
134 20559 gettimeofday({tv_sec=1514078472, tv_usec=740066}, NULL) = 0
135 20559 send(10, "G3nUPDATE piwigo_imagesn SET"..., 75, MSG_DONTWAIT) = 75
136 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
137 20559 recv(10, "012(Rows matched: 1 Cha"..., 2474, MSG_DONTWAIT) = 52
138 20559 gettimeofday({tv_sec=1514078472, tv_usec=745234}, NULL) = 0
139 20559 gettimeofday({tv_sec=1514078472, tv_usec=746016}, NULL) = 0
140 20559 send(10, "G3nUPDATE piwigo_imagesn SET"..., 75, MSG_DONTWAIT) = 75
141 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
142 20559 recv(10, "012(Rows matched: 1 Cha"..., 2422, MSG_DONTWAIT) = 52
143 20559 gettimeofday({tv_sec=1514078472, tv_usec=750938}, NULL) = 0
144 20559 gettimeofday({tv_sec=1514078472, tv_usec=751526}, NULL) = 0
145 20559 gettimeofday({tv_sec=1514078472, tv_usec=752395}, NULL) = 0
146 20559 gettimeofday({tv_sec=1514078472, tv_usec=752957}, NULL) = 0
147 20559 send(10, "R3nSELECT idn FROM piwigo_ca"..., 86, MSG_DONTWAIT) = 86
148 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
149 20559 recv(10, "111E23deftpiwigopix21piwigo_c"..., 2370, MSG_DONTWAIT) = 102
150 20559 gettimeofday({tv_sec=1514078472, tv_usec=758239}, NULL) = 0
151 20559 gettimeofday({tv_sec=1514078472, tv_usec=758945}, NULL) = 0
152 20559 send(10, "2053nSELECT id, path, represent"..., 137, MSG_DONTWAIT) = 137
153 20559 poll([{fd=10, events=POLLIN|POLLERR|POLLHUP}], 1, 1471228928) = 1 ([{fd=10, revents=POLLIN}])
154 20559 recv(10, "113=23deftpiwigopixrpiwigo_i"..., 2268, MSG_DONTWAIT) = 339
155 20559 gettimeofday({tv_sec=1514078472, tv_usec=764752}, NULL) = 0
156 20559 gettimeofday({tv_sec=1514078472, tv_usec=765603}, NULL) = 0
157 20559 gettimeofday({tv_sec=1514078472, tv_usec=766339}, NULL) = 0
158 20559 stat64("././galleries/family/Locallink.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
159 20559 getcwd("/srv/http/piwigo", 4096) = 17
160 20559 gettimeofday({tv_sec=1514078472, tv_usec=768178}, NULL) = 0
161 20559 lstat64("/srv/http/piwigo/././galleries/family/Locallink.jpg", {st_mode=S_IFLNK|0777, st_size=32, ...}) = 0
162 20559 readlink("/srv/http/piwigo/././galleries/family/Locallink.jpg", "/mnt/localfam/1977 Andrews_1.jpg", 4096) = 32
163 20559 lstat64("/mnt/localfam/1977 Andrews_1.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
164 20559 lstat64("/mnt/localfam", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
165 20559 lstat64("/mnt", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
166 20559 open("/mnt/localfam/1977 Andrews_1.jpg", O_RDONLY) = 11
167 20559 fstat64(11, {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
168 20559 _llseek(11, 0, [0], SEEK_CUR) = 0
169 20559 read(11, "37733037734020JFIF1111377333Crtnvn10r"..., 8192) = 8192
170 20559 close(11) = 0

And finally, the strace of mod_autoindex indexing a directory without including CIFSlink. File scanning at 43-48. Once again the successful files get scanned, then the single dot, then CIFSlink but once again it seems to get scanned in the end.

[alarm@alarmpi ~]$ nl indexstrace.txt | less
1 20536 _newselect(0, NULL, NULL, NULL, {tv_sec=1, tv_usec=0}) = 0 (Timeout)
2 20536 wait4(-1, 0x7ecec9f0, WNOHANG|WSTOPPED, NULL) = 0
3 20536 _newselect(0, NULL, NULL, NULL, {tv_sec=1, tv_usec=0} <unfinished ...>
4 20558 <... accept4 resumed> {sa_family=AF_INET6, sin6_port=htons(10914), inet_pton(AF_INET6, "::ffff:192.168.0.107", &sin6_addr), sin6_flowinfo=htonl(0), sin6_scope_id=0}, [128->28], SOCK_CLOEXEC) = 9
5 20558 getsockname(9, {sa_family=AF_INET6, sin6_port=htons(80), inet_pton(AF_INET6, "::ffff:192.168.0.100", &sin6_addr), sin6_flowinfo=htonl(0), sin6_scope_id=0}, [128->28]) = 0
6 20558 fcntl64(9, F_GETFL) = 0x2 (flags O_RDWR)
7 20558 fcntl64(9, F_SETFL, O_RDWR|O_NONBLOCK) = 0
8 20558 gettimeofday({tv_sec=1514078503, tv_usec=263541}, NULL) = 0
9 20558 read(9, "GET /family/ HTTP/1.1rnHost: 192"..., 8000) = 287
10 20558 gettimeofday({tv_sec=1514078503, tv_usec=264926}, NULL) = 0
11 20558 gettimeofday({tv_sec=1514078503, tv_usec=265863}, NULL) = 0
12 20558 gettimeofday({tv_sec=1514078503, tv_usec=266380}, NULL) = 0
13 20558 gettimeofday({tv_sec=1514078503, tv_usec=266905}, NULL) = 0
14 20558 gettimeofday({tv_sec=1514078503, tv_usec=267410}, NULL) = 0
15 20558 gettimeofday({tv_sec=1514078503, tv_usec=267897}, NULL) = 0
16 20558 gettimeofday({tv_sec=1514078503, tv_usec=268395}, NULL) = 0
17 20558 gettimeofday({tv_sec=1514078503, tv_usec=268985}, NULL) = 0
18 20558 gettimeofday({tv_sec=1514078503, tv_usec=269744}, NULL) = 0
19 20558 stat64("/srv/http/family/", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
20 20558 stat64("/srv/http/family/index.html", 0x7ecec600) = -1 ENOENT (No such file or directory)
21 20558 lstat64("/srv", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
22 20558 lstat64("/srv/http", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
23 20558 lstat64("/srv/http/family", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
24 20558 lstat64("/srv/http/family/index.html", 0x7ecec600) = -1 ENOENT (No such file or directory)
25 20558 stat64("/srv/http/family/index.php", 0x7ecec600) = -1 ENOENT (No such file or directory)
26 20558 lstat64("/srv", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
27 20558 lstat64("/srv/http", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
28 20558 lstat64("/srv/http/family", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
29 20558 lstat64("/srv/http/family/index.php", 0x7ecec600) = -1 ENOENT (No such file or directory)
30 20558 stat64("/srv/http/family/index.html", 0x7ecec600) = -1 ENOENT (No such file or directory)
31 20558 lstat64("/srv", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
32 20558 lstat64("/srv/http", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
33 20558 lstat64("/srv/http/family", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
34 20558 lstat64("/srv/http/family/index.html", 0x7ecec600) = -1 ENOENT (No such file or directory)
35 20558 open("/srv/http/family/", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 10
36 20558 fstat64(10, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
37 20558 stat64("/srv/http/family/HEADER.html", 0x7ecec4a0) = -1 ENOENT (No such file or directory)
38 20558 lstat64("/srv", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
39 20558 lstat64("/srv/http", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
40 20558 lstat64("/srv/http/family", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
41 20558 lstat64("/srv/http/family/HEADER.html", 0x7ecec4a0) = -1 ENOENT (No such file or directory)
42 20558 getdents64(10, /* 5 entries */, 32768) = 160
43 20558 lstat64("/srv/http/family/1977_Andrews_1.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
44 20558 lstat64("/srv/http/family/Locallink.jpg", {st_mode=S_IFLNK|0777, st_size=32, ...}) = 0
45 20558 stat64("/srv/http/family/Locallink.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
46 20558 lstat64("/srv/http/family/.", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
47 20558 lstat64("/srv/http/family/CIFSlink.jpg", {st_mode=S_IFLNK|0777, st_size=64, ...}) = 0
48 20558 stat64("/srv/http/family/CIFSlink.jpg", {st_mode=S_IFREG|0755, st_size=237934, ...}) = 0
49 20558 lstat64("/srv/http/family/..", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
50 20558 getdents64(10, /* 0 entries */, 32768) = 0
51 20558 close(10) = 0
52 20558 stat64("/srv/http/family/README.html", 0x7ecec4a0) = -1 ENOENT (No such file or directory)
53 20558 lstat64("/srv", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
54 20558 lstat64("/srv/http", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
55 20558 lstat64("/srv/http/family", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
56 20558 lstat64("/srv/http/family/README.html", 0x7ecec4a0) = -1 ENOENT (No such file or directory)
57 20558 gettimeofday({tv_sec=1514078503, tv_usec=311917}, NULL) = 0
58 20558 read(9, 0x3c9f60, 8000) = -1 EAGAIN (Resource temporarily unavailable)
59 20558 gettimeofday({tv_sec=1514078503, tv_usec=312941}, NULL) = 0
60 20558 writev(9, [{iov_base="HTTP/1.1 200 OKrnDate: Sun, 24 D"..., iov_len=218}, {iov_base="<!DOCTYPE HTML PUBLIC "-//W3C//D"..., iov_len=1112}], 2) = 1330
61 20558 write(7, "192.168.0.107 - - [23/Dec/2017:2"..., 80) = 80
62 20558 times({tms_utime=0, tms_stime=4, tms_cutime=0, tms_cstime=0}) = 953790583
63 20558 gettimeofday({tv_sec=1514078503, tv_usec=316096}, NULL) = 0
64 20558 poll([{fd=9, events=POLLIN}], 1, 5000 <unfinished ...>

The only vague thought remaining to me is that maybe there's some kind of timeout being tripped in the few milliseconds to get stuff over the CIFS share, but it seems like Apache of all servers should be fairly tolerant of latency. I don't think that has any real chance of being the answer and in any case I have no idea how to test it.