tencent cloud


Upload and Download

Last updated: 2022-06-20 14:38:12

    Does COS limit the upload and download bandwidth?

    Yes. The default bandwidth threshold for a single bucket residing in a public region in the Chinese mainland is 15 Gbps, and 10 Gbps for those in other regions. If this threshold is exceeded, bandwidth throttling will be triggered for requests. To raise the threshold, contact us.

    How can I directly preview a file in my browser without downloading it?

    You need to specify a correct Content-Type header for this file. In addition, the Content-Disposition parameter cannot be attachment. If the browser supports the current file format, it will directly open the file instead of downloading it.

    How do I directly download a file in my browser without previewing it?

    You can go to the COS console and set the value of the Content-Disposition in the custom object headers to attachment. For detailed directions, see Custom Headers.

    You can also set the value of the request parameter response-content-disposition in the GET Object API to attachment so that your browser can pop up a window for the file to be downloaded. For more information, see GET Object.


    To use the response-* parameter in a request, the request must be signed.

    How do I determine if I am accessing COS over a private network?

    The access endpoints of COS use intelligent DNS resolution. For COS access via the Internet (including different ISPs), we will detect and select the optimal linkage for you to access COS. If you have deployed a service in Tencent Cloud to access COS, access within the same region will be automatically directed to a private network address. Cross-region access is not supported in a private network and the COS endpoint is resolved to a public network address by default.

    How to determine access over a private network

    Tencent Cloud products within the same region access each other over a private network by default, incurring no traffic fees. Therefore, we recommend choosing the same region when you purchase different Tencent Cloud products to save on costs.

    The following shows how to determine access over a private network:

    For example, when a CVM accesses COS, to determine whether a private network is used for access, use the nslookup command on the CVM to resolve the COS endpoint. If a private IP is returned, access between the CVM and COS is over a private network; otherwise, it is over a public network.


    Generally, a private IP address takes the form of 10.*.*.* or 100.*.*.*, and a VPC IP address takes the form of 169.254.*.*.

    Assume that examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com is the address of the destination bucket; the Address: below indicates access is over a private network.

    nslookup examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com
    Address:  #53
    Name:   examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com
    Name:   examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com

    For more information about private and public network access and connectivity testing, see COS Access via Private Network and Public Network.

    For the private DNS server addresses of CVM, see Private Network DNS.


    The private IPs of Tencent Cloud BM instances may be different from those of CVM instances, and their formats are usually 9.*.*.* or 10.*.*.*. If you have any queries, contact us.

    How do I download a folder?

    You can log in to COSBrowser, select the folder to be downloaded, and click Download to download the folder or files in batches. You can also download a folder using the COSCMD tool. For more information, see COSCMD.

    What should I do if the error "403 Forbidden" occurs or access permission is rejected when I perform upload/download and other operations?

    You can troubleshoot by referring to A 403 Status Code is Returned When You Access COS.

    How do I upload or download multiple files using COS?

    COS allows you to upload or download multiple files through various methods such as the console, APIs/SDKs, and tools.

    When I upload a new file to a bucket in which another file of the same name exists, will the old file be overwritten or will the new file be saved with a different version name?

    The versioning feature is now available in COS. If versioning is not enabled for the bucket, when you upload a new file to a bucket in which another file of the same name already exists, the older one will be directly overwritten; if versioning is enabled, multiple versions of the object will co-exist.

    What is the minimum part size of a multipart upload in COS?

    1 MB. For more information, see Specifications and Limits.

    When uploading large files using multipart upload, can I replace an invalid signature to continue the multipart upload?


    How do I generate a temporary URL for files in COS?

    For more information, see Download via Pre-Signed URL.

    I have set a validity period for a signature, but why can it still be used to download objects after it has expired?

    By default, the browser will cache objects that have been loaded successfully. Therefore, if you access the same URL, the cached object will be returned without requesting the server again. Therefore, you are advised to use the Cache-Control: no-cache header during object upload to prevent browser caching (see PUT Object or Initiate Multipart Upload for details). Alternatively, you can specify the response-cache-control=no-cache request header during object download to prevent browser caching (see GET Object for details).

    What should I do if I upload a file in the console and "Upload failed due to network issues" is displayed?

    This error may occur due to an unstable local network environment. You can try the upload again in a different network environment.

    How do I prevent others from downloading my COS files?

    You can set your bucket permission to private read/write. For more information, see Setting Access Permission. You can also configure a hotlink protection allowlist on your bucket to block any access from endpoints that are not in the list. For more information, see Setting Hotlink Protection.

    Can I use case-insensitive download URLs?

    No. COS filenames are case-sensitive, and thus so are the download URLs. If you have enabled CDN acceleration for your bucket, you can go to the CDN console to configure Cache Ignore URL Case, which will increase the hit rate to some extent.

    What should I do if the error "your policy or acl has reached the limit (Status Code: 400; Error Code: PolicyFull)" occurs when I am uploading files or creating a bucket?

    COS allows each root account to have up to 1,000 bucket ACLs. If more bucket ACLs have been configured, this error will occur. Therefore, you can delete unnecessary bucket ACLs.


    You are not advised to use object-level ACLs or policies. When calling APIs or SDKs, if you do not need ACL control over a file, we recommend leaving the ACL-related parameters (such as x-cos-acl and ACL) empty to inherit the bucket permissions.

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