工作了好几年，但突然停了下来。显然，环境一定发生了变化，但我需要一些想法来决定该往哪里看
Linux 工作站从 Windows AD 域中的 NAS 设备自动挂载 SMB 共享
Fedora 32
内核 5.7.8-200.fc32.x86_64
mount.cifs 版本：6.9
auto.misc 条目示例：
it-share -fstype=cifs,multiuser,cruid=${UID},rw,vers=default,sec=krb5 ://filer5/IT_Share
上例中目标 (filer5) 是 QNAP TS-870U-RP 版本 4.3.6.1070 (2019/09/10) NAS 设备，但其他 NAS 设备也存在同样的问题
dmesg：
[77285.466321] fs/cifs/cifsfs.c: Devname: //filer5/IT_Share flags: 0
[77285.466353] fs/cifs/connect.c: Username: root
[77285.466355] fs/cifs/connect.c: file mode: 0755 dir mode: 0755
[77285.466358] fs/cifs/connect.c: CIFS VFS: in mount_get_conns as Xid: 18 with uid: 0
[77285.466359] fs/cifs/connect.c: UNC: \\filer5\IT_Share
[77285.466367] fs/cifs/connect.c: Socket created
[77285.466369] fs/cifs/connect.c: sndbuf 16384 rcvbuf 131072 rcvtimeo 0x1b58
[77285.466722] fs/cifs/fscache.c: cifs_fscache_get_client_cookie: (0x0000000003004025/0x000000002aa94fc9)
[77285.466724] fs/cifs/connect.c: Demultiplex PID: 15612
[77285.466728] fs/cifs/connect.c: CIFS VFS: in cifs_get_smb_ses as Xid: 19 with uid: 0
[77285.466729] fs/cifs/connect.c: Existing smb sess not found
[77285.466734] fs/cifs/smb2pdu.c: Negotiate protocol
[77285.466753] fs/cifs/transport.c: Sending smb: smb_len=228
[77285.613638] fs/cifs/connect.c: RFC1002 header 0x11c
[77285.613649] fs/cifs/smb2misc.c: SMB2 data length 96 offset 128
[77285.613650] fs/cifs/smb2misc.c: SMB2 len 224
[77285.613652] fs/cifs/smb2misc.c: length of negcontexts 60 pad 0
[77285.613695] fs/cifs/transport.c: cifs_sync_mid_result: cmd=0 mid=0 state=4
[77285.613737] fs/cifs/misc.c: Null buffer passed to cifs_small_buf_release
[77285.613742] fs/cifs/smb2pdu.c: mode 0x1
[77285.613744] fs/cifs/smb2pdu.c: negotiated smb3.1.1 dialect
[77285.613752] fs/cifs/asn1.c: OID len = 7 oid = 0x1 0x2 0x348 0xbb92
[77285.613755] fs/cifs/asn1.c: OID len = 7 oid = 0x1 0x2 0x348 0x1bb92
[77285.613757] fs/cifs/asn1.c: OID len = 10 oid = 0x1 0x3 0x6 0x1
[77285.613759] fs/cifs/smb2pdu.c: decoding 2 negotiate contexts
[77285.613761] fs/cifs/smb2pdu.c: decode SMB3.11 encryption neg context of len 4
[77285.613763] fs/cifs/smb2pdu.c: SMB311 cipher type:1
[77285.613767] fs/cifs/connect.c: Security Mode: 0x1 Capabilities: 0x300046 TimeAdjust: 0
[77285.613769] fs/cifs/smb2pdu.c: Session Setup
[77285.613771] fs/cifs/smb2pdu.c: sess setup type 5
[77285.613785] fs/cifs/cifs_spnego.c: key description = ver=0x2;host=filer5;ip4=10.1.123.38;sec=krb5;uid=0x0;creduid=0x3e8;user=root;pid=0x3cfa
[77285.626771] CIFS VFS: \\filer5 Send error in SessSetup = -126
[77285.626775] fs/cifs/connect.c: CIFS VFS: leaving cifs_get_smb_ses (xid = 19) rc = -126
[77285.626777] fs/cifs/connect.c: build_unc_path_to_root: full_path=\\filer5\IT_Share
[77285.626778] fs/cifs/connect.c: build_unc_path_to_root: full_path=\\filer5\IT_Share
[77285.626779] fs/cifs/connect.c: build_unc_path_to_root: full_path=\\filer5\IT_Share
[77285.626781] fs/cifs/dfs_cache.c: __dfs_cache_find: search path: \filer5\IT_Share
[77285.626782] fs/cifs/dfs_cache.c: get_dfs_referral: get an DFS referral for \filer5\IT_Share
[77285.626783] fs/cifs/dfs_cache.c: dfs_cache_noreq_find: path: \filer5\IT_Share
[77285.626791] fs/cifs/fscache.c: cifs_fscache_release_client_cookie: (0x0000000003004025/0x000000002aa94fc9)
[77285.626796] fs/cifs/connect.c: CIFS VFS: leaving mount_put_conns (xid = 18) rc = 0
[77285.626797] CIFS VFS: cifs_mount failed w/return code = -2
日志控制：
cifs.upcall[15613]: key description: cifs.spnego;0;0;39010000;ver=0x2;host=filer5;ip4=10.1.123.38;sec=krb5;uid=0x0;creduid=0x3e8;user=roo>
cifs.upcall[15613]: ver=2
cifs.upcall[15613]: host=filer5
cifs.upcall[15613]: ip=10.1.123.38
cifs.upcall[15613]: sec=1
cifs.upcall[15613]: uid=0
cifs.upcall[15613]: creduid=1000
cifs.upcall[15613]: user=root
cifs.upcall[16103]: get_cachename_from_process_env: pathname=/proc/16100/environ
cifs.upcall[16103]: get_existing_cc: default ccache is KEYRING:persistent:1000:1000
cifs.upcall[16103]: handle_krb5_mech: getting service ticket for filer5
cifs.upcall[16103]: cifs_krb5_get_req: unable to get credentials for filer5
cifs.upcall[16103]: handle_krb5_mech: failed to obtain service ticket (-1765328370)
cifs.upcall[16103]: handle_krb5_mech: getting service ticket for filer5.example.org
cifs.upcall[16103]: cifs_krb5_get_req: unable to get credentials for filer5.example.org
cifs.upcall[16103]: handle_krb5_mech: failed to obtain service ticket (-1765328370)
cifs.upcall[16103]: ip_to_fqdn: resolved 10.1.123.38 to filer5.EXAMPLE.ORG
cifs.upcall[16103]: handle_krb5_mech: getting service ticket for filer5.example.org
cifs.upcall[16103]: cifs_krb5_get_req: unable to get credentials for filer5.example.org
cifs.upcall[16103]: handle_krb5_mech: failed to obtain service ticket (-1765328370)
cifs.upcall[16103]: Unable to obtain service ticket
cifs.upcall[16103]: Exit status -1765328370
cifs.upcall 似乎无法检索 uid 1000 的 kerberos 会话密钥。或者目标不接受这些缓存的凭据。据我所知，这些凭据似乎确实存在
$ klist
Ticket cache: KEYRING:persistent:1000:1000
Default principal: [email protected]
Valid starting Expires Service principal
07/18/2020 06:41:02 07/18/2020 16:41:02 krbtgt/[email protected]
renew until 07/25/2020 06:40:53
尝试在 /etc/hosts 中为 filer5 添加静态条目，并在 /etc/request-key.d/ 中为 cifs.upcall 的调用添加“-t”选项，以防这可能与 DNS 相关，但结果没有变化
没有对 AD 或 DNS 配置进行任何已知更改。没有对 NAS 设备应用固件升级。仅对 Fedora 工作站应用标准 dnf/yum 更新。
如果您能提供关于在哪里（以及如何）进一步排除故障的建议，我们将不胜感激。\
答案1
我遇到过类似的情况，并认为这是最近内核的退化。我已提交错误报告，但与此同时我发现降级到5.7.7（或5.4.50降级为-lts内核）可以避免此问题。